Pit-building Antlion Larvae Research Articles

Optimal pit site selection in antlion larvae: the relationship between prey availability and pit maintenance costs

Traps are an efficient method of capturing prey for ambush predators, but trap building and maintenance are costly. We describe suitable hunting sites for pit-building antlion larvae living in sand dunes based on its cost–benefit relationship. In the field, antlion pits were located near natural barriers, such as cliffs, rocks and vegetation, but not closest to these barriers. Our results show that this pattern of pit location did not differ between populations; neither with or without the influence of a specific dipteran parasitoid of antlion larvae. Artificial pitfall traps deployed in their habitats revealed that invertebrates move along barriers, likely through thigmotaxis (wall hugging or wall-following), and drop sands in the traps set at barrier edges. In the laboratory, repeated artificial destruction of pits from larval antlions induced frequent pit relocation and rebuilding. This task reduces life history parameters, such as the larval growth and food conversion rates, suggesting a high cost of pit maintenance. Thus, antlion pits might shift away from barrier edges where more prey is available but pit destruction occurs more frequently due to wall-following invertebrates. Such disturbance may explain why antlions are not located closest to these barriers.

Sand-throwing behaviour in pit-building antlion larvae: insights from finite-element modelling.

Sandy pitfall traps of antlions are elaborate constructions to capture prey. Antlions exploit the interactions between the particles in their habitat and build a stable trap. This trap is close to the unstable state; prey items will slide towards the centre-where the antlion ambushes-when entering the trap. This is efficient but requires permanent maintenance. According to the present knowledge, antlions throw sand, mainly to cause sandslides towards the centre of the pit. We hypothesized that: (i) sand-throwing causes sandslides towards the centre of the pit and (ii) sand-throwing constantly maintains the pitfall trap and thus keeps its efficiency high. Using laboratory experiments, as well as finite-element analysis, we tested these hypotheses. We show, experimentally and numerically, that sand that accumulates at the centre of the pit will be removed continuously by sand-throwing, this maintenance is leading to slope condition close to an unstable state. This keeps the slope angle steep and the efficiency of the trap constant. Furthermore, the resulting sandslides can relocate the trapped prey towards the centre of the pit. This study adds further insights from specific mechanical properties of a granular medium into the behavioural context of hunting antlion larvae.

Sand-throwing behaviour in pit-building antlion larvae: insights from finite element modelling

Sand-throwing behaviour in pit-building antlion larvae: insights from finite element modelling

Soil moisture preference in the antlion Baliga micans (Neuroptera: Myrmeleontidae)

Pit-building antlion larvae require not only dry and loose sand, but also other abiotic factors for beneficial pit site selection. Although wet soil is generally avoided by antlions, we assumed that antlion larvae of Baliga micans (McLachlan) (Neuroptera: Myrmeleontidae) prefer some degree of soil moisture because their relatively higher respiratory rate may cause water loss. We conducted behavioral experiments for pit construction in soils of different moisture content (0–29%) to quantitatively clarify soil moisture preference. Under the control containing only dry soil, some larvae died, no pits were frequently found, and larval weight decreased. The larvae constructed pits on the wet soil more frequently than on the dry soil. Particularly, the 2nd- and 3rd-instar larvae preferred the 9% soil and the 17% soil moisture, respectively. Therefore, the larvae showed soil moisture preference, owing to a probable physiological constraint. The soil moisture preference that secures the survival period is possibly a requisite trait for effective foraging.

Fine sand particles enable antlions to build pitfall traps with advanced three-dimensional geometry.

Pit-building antlion larvae are predators that construct pitfall traps in fine sand. We used three-dimensional laser scanning and geometric morphometrics to reveal the shape of antlion pits of two antlion species, analysed the particle size composition of sands from the different natural habitats, and measured the slope angles of the pits of the two species. In most antlions, the pits are structured as a simple inverted cone, as in Myrmeleon hyalinus, studied here. The other antlion studied, Cueta lineosa, constructs a unique pit composed of two inverted truncated cones inserted into one another, which feature substantially steeper walls than the pits of any other antlion studied to date. Pit stability depends on the slope inclination, which oscillates between the maximum angle of stability and the angle of repose. The angles in C. linosa substrates were larger than those in M. hyalinus substrates. One reason for the steeper walls is the greater proportion of fine sand in the natural sand inhabited by C. lineosa However, video-recording revealed that both the natural sand of C. lineosa and the finest sand tested had a higher maximum angle of stability than any of the other substrates studied here. Furthermore, experiments with pits built in different substrates revealed that the shape of the pit is variable and depends on the structure of the sand. Myrmeleonhyalinus displayed a more flexible pit construction behaviour than C. lineosa The present demonstration of such differences in pit characteristics contributes to understanding how these two species co-exist in the same habitat.

Behavioral repeatability and personality in pit-building antlion larvae under differing environmental contexts

Over the last decades, there has been growing interest among behavioral ecologists in exploring animal personalities. However, while the foraging behavior of active foragers has been extensively studied, only little is known about that of sit-and-wait predators within the personality framework. We investigated the existence of repeatability and personality in pit-building antlion larvae in the context of foraging (pit construction) and habitat selection (relocation distance and direction) over time and under three environmental contexts: thermal conditions, sand depth, and soil type. Over time, repeatability was much stronger for relocation distance than for movement directionality. Additionally, we observed positive correlations across the two levels of sand depth and soil type but not between thermal conditions. Change in substrate type may induce faster decision-making in these sand-dwelling insects or could be perceived by such insects as a more drastic alteration in their habitat. We suggest that different individuals indeed possess distinct personalities. We also suggest that repeatability should be measured at two levels: the amount of energy expenditure (distances and pit construction) and the pattern of energy expenditure (directionality). Finally, our study illustrates how differing environmental conditions can result in differing levels of plasticity, while largely preserving individual personalities.

Dangerous neighbors: interactive effects of factors influencing cannibalism in pit-building antlion larvae

Cannibalism is a common trophic interaction in size-structured populations, having important ramifications for population and community dynamics. Although the main factors potentially influencing cannibalism are apparently well investigated, relatively little is known on how these factors interact to influence the frequency of cannibalism. We performed 2 complementary experiments to test if cannibalism in larvae of the pit-building antlion Myrmeleon hyalinus is influenced by size differences within and between developmental stages, as well as by sand depth (potential refuge), conspecific density, and hunger level. Our working hypothesis was that cannibalism should act as a threshold event governed by the interactive (rather than additive) effects of intrinsic and extrinsic factors. As expected, the frequency of cannibalism was higher between than within developmental stages, with more advanced instar larvae feeding on smaller instars. Notably, decreased density significantly lowered the frequency of cannibalism; however, this pattern was evident only in deep sand, which provides a potential refuge from predators. Deep sand also lessened the positive effect of body size difference on the frequency of cannibalism. Hunger level increased the frequency of cannibalism; however, the identity of the cannibal was almost exclusively determined by its initial size advantage rather than by its hunger level. Our results demonstrate that, despite their sedentary nature, the frequency of cannibalism in pit-building antlion larvae can be relatively high. Furthermore, this trophic interaction is governed by the interactive rather than additive effects of intrinsic and extrinsic factors influencing cannibalism.

Consequences of the instar stage for behavior in a pit-building antlion

Pit-building antlion larvae are opportunistic predators that dig conical pits in loose soils, and prey on small arthropods that fall into their traps. We investigated different behavioral traits of second and third instar larvae selected for similar body masses, while also exploring the behavioral consistency and personalities of the third instar stage. Second instar larvae constructed smaller pits than third instar larvae. The former also responded more slowly to prey and exploited prey less efficiently. Notably, all these instar-based differences disappeared after molting into the third instar stage. In addition, third instar larvae exhibited consistent behavior in their pit size, response times to prey and to less extent in relocation distances. We detected two axes of behavior. The first axis included a correlation between pit size, response time and prey exploitation efficiency, thus reflecting investment in foraging activity. The second axis seemed to represent a trade-off between response time and relocation distance, implying that individuals that responded more slowly to prey, relocated over larger distances. These results point to coordinated behavior reflecting different levels of investment in foraging, while also emphasizing the importance of instar stage, in addition to body mass, when studying the behavior of such organisms characterized by a complex life cycle.

Jack of All Trades, Master of All: A Positive Association between Habitat Niche Breadth and Foraging Performance in Pit-Building Antlion Larvae

Species utilizing a wide range of resources are intuitively expected to be less efficient in exploiting each resource type compared to species which have developed an optimal phenotype for utilizing only one or a few resources. We report here the results of an empirical study whose aim was to test for a negative association between habitat niche breadth and foraging performance. As a model system to address this question, we used two highly abundant species of pit-building antlions varying in their habitat niche breadth: the habitat generalist Myrmeleon hyalinus, which inhabits a variety of soil types but occurs mainly in sandy soils, and the habitat specialist Cueta lineosa, which is restricted to light soils such as loess. Both species were able to discriminate between the two soils, with each showing a distinct and higher preference to the soil type providing higher prey capture success and characterizing its primary habitat-of-origin. As expected, only small differences in the foraging performances of the habitat generalist were evident between the two soils, while the performance of the habitat specialist was markedly reduced in the alternative sandy soil. Remarkably, in both soil types, the habitat generalist constructed pits and responded to prey faster than the habitat specialist, at least under the temperature range of this study. Furthermore, prey capture success of the habitat generalist was higher than that of the habitat specialist irrespective of the soil type or prey ant species encountered, implying a positive association between habitat niche-breadth and foraging performance. Alternatively, C. lineosa specialization to light soils does not necessarily confer upon its superiority in utilizing such habitats. We thus suggest that habitat specialization in C. lineosa is either an evolutionary dead-end, or, more likely, that this species' superiority in light soils can only be evident when considering additional niche axes.

The involvement of sand disturbance, cannibalism and intra-guild predation in competitive interactions among pit-building antlion larvae

Competition in trap-building predators such as antlion larvae is a complex biotic interaction, potentially involving exploitation competition, sand throwing (i.e., interference competition), cannibalism and intra-guild predation. We investigated the short-term behavioral and developmental responses of the strict sit-and-wait antlion predator Myrmeleon hyalinus to sand disturbance (i.e., quantification of the impact of severe sand throwing), and to con- and hetero-specific competition by a larger sit-and-pursue antlion species Lopezus fedtschenkoi. We found that antlions subjected to sand disturbances reduced their pit construction activity and relocated less often. Furthermore, the reduction in pit construction activity was stronger among antlions subjected to disturbances prior to feeding. Almost no death occurred during the sand disturbance experiment, but as expected, disturbances caused reductions in the relative growth rates of antlions. This negative effect was stronger in the group exposed to sand disturbances prior to feeding. The presence of the sit-and-pursue competitor led to reductions both in pit construction and in relocation activities of M. hyalinus. Although the per-capita food supply was identical in both experiments, only 48% of M. hyalinus larvae survived the competition experiment, and this pattern was consistent between the con- and hetero-specific treatments. However, in the presence of hetero-specific competitors, the relative growth rate of surviving larvae was significantly lower than that measured in the presence of con-specific competitors. Our study demonstrates that investigating the different components of complex biotic interactions can markedly improve our understanding of how these different factors interact to influence the behavior and life history of organisms.

Response of pit-building antlions to repeated unsuccessful encounters with prey

Pit-building antlion larvae are sit-and-wait predatory insects that construct conical pits, from which they ambush prey, in sandy soils. We examined the behavioural responses of antlions to the detection of various sized prey, which they were not allowed to capture. We found that antlions responded faster to smaller prey items, probably because larger prey may be considered a source of disturbance rather than a food source. Antlion response time to provided prey decreased after feeding and was negatively correlated with antlion body mass. Both of these results were indicative of a response to prey that depended on both internal and external factors. Pit dimensions increased with time at a constant rate among antlions in the unsuccessful prey capture or fed groups, but at a decelerating rate in the unfed control group. Contrary to our expectation, we could not detect differences in the rate of mass loss between antlions that were unfed and those experiencing unsuccessful prey captures. We also posited that antlions should exploit a specific prey type more efficiently as the number of encounters they had with it increased. However, there was no support for this prediction in our study. Exploring the responses of predators to prey in general, and in light of the conditions characterizing their natural habitat in particular, can improve our understanding of how predators adapt to cope with environmental variability.

Sub-optimal pit construction in predatory ant lion larvae ( Myrmeleon sp.)

The impacts on energy gains of two aspects of ant lion pit architecture were investigated in a natural population of pit-building ant lion larvae ( Myrmeleon sp.) in Costa Rica. Field and laboratory settings were used to examine the impacts of circumference and depth of the pit on net energy gain rate. An optimization model predicted a point optimum circumference and angle of depression in an unconstrained system, and positive correlations between body mass, pit circumference, and pit angle of depression in the presence of physiological constraints on both measures. Such a physiological constraint is possible in this system due to a large one-time construction cost. All of these correlations were observed in a lab setting with filtered substrate and no competition; though none were significant in the field. Individuals additionally constructed wider, shallower pits in the field. These results are consistent with an angle of depression that is limited by the angle of repose of the substrate in the field, rather than physiology. These results provided suggestive evidence for sub-optimal pit dimensions in Myrmeleon sp., and for the importance of substrate type in understanding the architecture of natural ant lion pits. The model predicted that the frequency of relocation would not affect the optimal angle of depression, but it would affect the optimal pit circumference to a degree proportional to the square root of the change in the average time an ant lion occupies a single pit. These findings challenge the widely held assumption of adaptive optimality in animal foraging.

Foraging behaviour and habitat selection in pit-building antlion larvae in constant light or dark conditions

Pit-building antlion larvae are small sit-and-wait arthropod predators that dig conical pits in sandy soils. We investigated the effect of exposure to constant light versus constant dark conditions on antlion behaviour. Antlions tended to relocate less often, construct pits more frequently and construct larger pits in constant light. We interpret this as an indication of dichotomous behaviour under light versus dark conditions such that antlion larvae hunt during the day and modify their positions at night. Antlion larvae immediately responded to the complete switch in this illumination treatment and adapted their behaviour to fit the new conditions. Prey capture success did not differ between the constant light and constant dark conditions. When provided with a choice between light and dark conditions, the vast majority of larvae preferred the former. Those that preferred constant dark, however, were on average larger than those that preferred constant light. We thus suggest that since larger antlion larvae possess larger fat reserves, they can afford reductions in foraging activity (possibly to increase safety). An examination of the antlion trade-off between their preference for light and their preference for sand depth (which may affect their ability to evade predators) showed that their response to illumination was much more prominent, irrespective of the sand depth. Finally, combining light with other factors such as temperature and density may further elucidate microhabitat selection in pit-building antlion larvae.

Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae

There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.

Pit building ant-lion larvae effect to the distribution of the substrate particles in their microhabitats

The distribution of the size of the substrate particles in and around the pits of the pit-building antlion larvae was examined at two different types of microhabitats (open and protected). Samples of substrate were taken from the side of the pits, from the edges of the pits and from 3 cm and 10 cm away from the edges of the pit. The size of the substrate particles taken 10 cm away from the edge is considered to be characteristic for the microhabitat. The samplings consisted of different quality of substrates such as sand, loess, clay and they were taken at all three larvae stages. The samples were divided into fractions by a sieve series and the distribution of the weight percentage of the granulation was analyzed. In order to compare the samples the cluster analysis and statistical tests were used. The preference calculations were performed with Ivlev's index of preference (Ei minimum -1; Ei maximum +1). In this respect the distribution of sandy area in the Carpathian Basin is in correspondence with the distribution of the pit-building ant-lion larvae living in open habitats. The preference of the ant-lion larvae living in protected habitat does not depend on the bedrock. The investigation proved that the substrate has particular spatial distribution in the pits and their environment (microhabitat). While building and repairing the pit, the larvae gather the fine particles in the pit and throw the bigger particles further out from the pit. The spatial distribution of the particle size of the substrate can be actively influenced by the chitin bristles and teeth of the mandibles and head of the larvae. Statistical analysis has proved that the particle size preference does not depend on the development stage of the larvae, it is not species dependent and it does not depend on the quality of the substrate as well. The preferred particle size of the pit-building ant-lion larvae was determined by the physical characteristics (particle size, to what extent they were cemented) of the substrate (sand, loess, clay) which is typical of the habitat. The present and the earlier studies suggest that Euroleon nostras, and very likely other pit-building species living in protected microhabitat, chose their habitats providing less food besides optimal particle size and thermal conditions. On the other hand, the species occurring in open habitats such as Myrmeleon bore, live in habitats with bigger food supply but with extreme thermal conditions and coarser particle size.

Temperature Tolerance and Predatory Strategy of Pit-Building Ant-Lion Larvae (Neuroptera: Myrmeleontidae)

This study focuses on the nocturnal and diurnal temperature relations inside and around the pits of Myrmeleon bore pit-building ant-lion larvae living in unsheltered microhabitat and Euroleon nostras living in sheltered microhabitat. The larvae's potential hunting activity and prey handling phase of predation in relation to the temperature conditions were observed. Due to the structure of pitfalls and the thermal layers above and under the sand surface, the larvae must suffer less temperature fluctuation during the day than their environment. The role of the pitfall seems to be just as important in prey capturing as in temperature tolerance. This function of pits especially prevails in unsheltered microhabitats. In unsheltered microhabitats temperature influences the potential predator activity as well as the distribution of prey handling phase of predation in time. The potential hunting activity of larvae is not influenced by temperature in sheltered microhabitats, where their prey handling phase of pred...

Comparative study on the behavioral response to starvation in three species of antlion larvae (Neuroptera: Myrmeleontidae)

To clarify how pit-building antlion larvae behave during prolonged periods of low resource abundance, pit relocation rate, giving-up time, and respiration rate under starvation conditions were examined, using three species of antlion larvae. Most larvae ofMyrmeleon bore never relocated their pits before they starved to death, while larvae ofHagenomyia micans relocated more often thanMyrmeleon formicarius (average number of pit relocations 0.04 forM. bore, 0.19 forM. formicarius, and 0.62/individual/10 days forH. micans). The relative respiration rate, a ratio of respiration rate at starvation to that at satiation, was lower inM. bore andM. formicarius than in H. micans. Thus, there was an inversely proportional relationship between the pit relocation rate and the decrease in respiration rate under starvation conditions in the three species of antlion larvae.