Redback Spider Research Articles

Redback spider bite: Signs, symptoms and sequelae

Redback spider bite: Signs, symptoms and sequelae

Female's courtship threshold allows intruding males to mate with reduced effort.

Female decision rules can influence the nature and intensity of sexual selection on males, but empirical demonstrations of rules underlying choice are rare. We hypothesized that female choice is largely based on a courtship duration threshold in the Australian redback spider (Latrodectus hasselti) because females kill males before copulation is complete (premature cannibalism) and reduce their paternity if courtship is brief. We used published data to infer that the female's threshold is approximately 100 min of courtship. We support this hypothesis by showing that premature cannibalism is common when the male's courtship duration is below this threshold, but is infrequent and unrelated to duration once courtship exceeds the threshold. We then ask whether females discriminate the source of courtship when rival males compete, as this will determine the effect of the threshold on male competitive tactics. We staged competitions where 'resident' males initially courted females in the absence of competition, exceeding the courtship threshold before 'intruding' males were introduced. Intruding males mated rapidly but were not prematurely cannibalized by females, in contrast to cases where competition starts before the threshold is surpassed. This suggests females do not distinguish which male satisfies the threshold, allowing intruders to parasitize the courtship efforts of residents. To our knowledge, such exploitation of mating efforts by rival males mediated by a female choice threshold has not been demonstrated elsewhere. Ironically, this female choice threshold and the attendant possibility of courtship parasitism may lead to selection for lower-quality males to recognize and seek out (rather than avoid) webs in which competitors are already present.

A sneaky spider

Journal of Paediatrics and Child HealthVolume 45, Issue 7-8 p. 477-477 A sneaky spider First published: 31 July 2009 https://doi.org/10.1111/j.1440-1754.2009.01558.x Sue Gorton, remote PhD student, School of Education, James Cook University, Townsville (susan.gorton@jcu.edu.au) Commentary: Treating redback spider envenoming – the evidence, the interpretation and current thinking Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume45, Issue7-8July/August 2009Pages 477-477 RelatedInformation

Body condition but not dietary restriction prolongs lifespan in a semelparous capital breeder

Effects of diet on longevity are complex because acquired resources are shared among growth, reproduction and somatic maintenance. We simplify these axes by examining how dietary restriction and competitive contexts affect longevity using semelparous males of the Australian redback spider (Latrodectus hasselti). Plastic development of L. hasselti males results in trade-offs of body condition against faster development if females are present, facilitating scramble competition. In the absence of females, males develop slowly as high body condition adults, and are better equipped for mate searching. Here we focus on effects of diet and competitive context on body condition and longevity. Although male survival depended on body condition and exercise, contrary to studies in a wide range of taxa, dietary restriction did not increase longevity. However, there was an interactive effect of diet and competitive context on lifespan, because high-diet males reared in the absence of females lived longer than males reared in the presence of females. Thus males near females pay a survival cost of developing rapidly. This shows that life-history trade-offs affected by competitive context can impose longevity costs independent of the direct energy expenditure of searching, courtship, competition or reproduction.

Australian immigrant of the arachnid variety?

Spider bites are an uncommon presenting complaint to Irish emergency services. We describe the case report of a patient diagnosed with a spider bite, thought due to an Australian (White-Tailed) spider unintentionally imported in a traveller's luggage. Her lesions were consistent with those caused by White-Tailed Spiders, and her clinical course and management is described. We subsequently present a review of the literature regarding spider bites. The most recent comprehensive catalogue of Irish arachnids, published by van Helsdingen, included 397 species. At least nine of these are exotic species, thought to have immigrated via importations, and in some cases surviving in hot-house environments. Although Irish native spiders are not generally noxious and cause only minor effects, immigrants may potentially cause harm. White-Tailed (Lamponidae) and Redback (Lacrodectus) spiders are common Australian species, and the clinical features experienced by victims of their bites are described. The identification and management of spider bites continue to be a source of heated debate and controversy. The ascription of various clinical effects to particular spiders is problematic because of poor case definition and a lack of confirmed scientific evidence. However, spider bite enquiries are now the single most common reason for calls to Australian poisons centres. The diagnosis and treatment of spider bites is discussed with reference to the use of antibiotics, steroids and antivenoms, as featured in the recent literature.

Commercial monovalent antivenoms in Australia are polyvalent

Monovalent antivenoms have a lower volume of specific antibodies that may reduce reactions but require accurate snake identification to be used. Polyvalent antivenoms are larger volume and may have a higher reaction rate. However, they avoid the problem of snake identification and may be more cost-effective to manufacture. We have previously shown cross-neutralisation of two Australian elapid venoms, tiger snake ( Notechis scutatus) and brown snake ( Pseudonaja textilis) venoms, by their respective monovalent antivenoms. In this study enzyme immunoassays were used to quantify the amount of monovalent antivenom (quantity of monovalent antibodies to a specific snake venom) in vials of commercially produced antivenom in Australia. All antivenoms tested appeared to be polyvalent and contain varying amounts of all five terrestrial snake monovalent antibodies based on their binding to the five representative venoms. Redback spider antivenom did not have any measurable binding affinity for any of the five snake venoms, showing that the observed binding is not due to non-specific interactions with equine protein. The antivenoms had expiry dates over a 15 year period, suggesting that the antivenoms have been mixtures for at least this time. This study cannot be used to rationalise hospital stocks of antivenom in Australia because there is no guarantee that the antivenoms will remain as mixtures. However, it would be possible for the manufacturer to reduce the number of types of snake antivenoms available in Australia to two polyvalent antivenoms which would simplify treatment of snakebite.

A change in competitive context reverses sexual selection on male size

In studies of sexual selection, larger size is often argued to increase male fitness, and relatively smaller males are explained by genetic and/or environmental variation. We demonstrate that a size-development life-history trade-off could underlie the maintenance of a broad, unimodal distribution of size in male redback spiders (Latrodectus hasselti). Larger males are superior in direct competition, but redback males mature rapidly at small size in the presence of females. In field enclosures, we simulated two competitive contexts favouring development of divergent male sizes. Relatively smaller males lost when competing directly, but had 10 times higher fitness than relatively larger males when given the temporal advantage of rapid development. Linear selection gradients confirmed the reversal of selection on size, showing that it is critical to consider life-history decisions underlying the development of traits related to fitness.

Subtle pedipalp dimorphism: a reliable method for sexing juvenile spiders

Quantifying primary sex ratios is necessary for studies in a wide range of areas including adaptive sex ratio modification, population demography, and sex-biased developmental mortality. Adult and penultimate male spiders are easy to sex, due to the great thickening of the male pedipalps, which are used for delivering sperm to the female reproductive tract. However, in many spider species, males and females are apparently monomorphic at hatching, are difficult to rear, and cannibalize their siblings, making assessment of primary sex ratios problematic. One technique for sexing spiders is karyotyping, but this can be challenging and time-consuming, particularly for species with high fecundity, and often requires destructive sampling. Here we report that, although apparently monomorphic, early-instar juveniles of two species of black widow spiders (Latrodectus hasselti Thorell 1870 and Latrodectus hesperus Chamberlin & Ivie 1935) can be sexed reliably. Palp width measurements are significantly different for males and females at the 3rd instar, with the palpi of juvenile females thinner than those of males. Moreover, sex identification with 89-100% accuracy can be achieved by an experienced observer visually inspecting the palpi of 3rd instar spiderlings under a dissecting microscope. Our results suggest that minimal investment in a pilot study can yield an accurate method for sexing juvenile spiders in the laboratory or field. The suitability of this method should be examined in other species with apparently monomorphic spiderlings, particularly those in which adult males have significantly enlarged palpi.

Male courtship effort determines female response to competing rivals in redback spiders

When males compete with rivals in the presence of females, there may be a trade-off between courtship and competition. We examined responses of female redback spiders, Latrodectus hasselti, to courtship from rival males under different competitive contexts. We paired size-matched males with females, and assessed correlates of male mating success. We compared these results to published data between females and single males or size-mismatched rivals. Size-matched males attempted copulation after a brief courtship, a strategy similar to smaller, ‘sneaker’ males in size-mismatched competitions. We also found context-dependent differences in female remating frequency and premature cannibalism. In sizemismatched and single-male trials, females prematurely cannibalized smaller males and males that mated quickly, but this was not the case when rivals were size-matched. However, in both types of competitive trials, males that mated rapidly paid a fitness cost. The courtship duration of the first male to mate was inversely related to the number of copulations that females accepted from that male’s rival. Thus, females use premature cannibalism to reduce the paternity of males that minimize investment in courtship if they are clearly distinguishable from their rivals (mismatched context), but they allow males to continue to compete if they are similar in quality (matched context). In both cases, biases in female remating behaviour favoured males that invested in courtship. We conclude that female reproductive behaviour partly depends on the relative size of competing males, but that male fitness depends heavily on investment in courtship.

Mated Redback Spider Females Re‐Advertise Receptivity Months after Mating

AbstractIn many species, selection acts on males to recognize female reproductive status at a distance using pheromones. Unmated females may actively seek to attract males; however, mated females may become cryptic to avoid attracting additional males if multiple matings are costly. Although females of many species cease pheromone production after mating, it is often unclear whether this is a strategic part of a female reproductive strategy, or whether this is because of chemical manipulation by males. If variation in pheromone production is part of the female’s strategy, then we predicted mated females should eventually re‐advertise receptivity if the benefits of multiple mating increase with time since copulation (e.g. because of sperm depletion). Here, we tested this prediction in Australian redback spiders (Latrodectus hasselti). First, we replicated earlier results by showing that virgin males discriminate female maturity and mating status based exclusively on web‐borne chemicals. Our results show this difference must arise from a change in chemical deposition in the web as we controlled for web volume differences between mated and virgin females. Male activity on extracts from webs of virgin females exceeded activity on a solvent control and on extracts of webs of just‐mated females—confirming that female redbacks cease pheromone production immediately after mating. Second, we tested a new prediction that mated females might re‐advertise receptivity near the end of their normal breeding season to replenish diminished sperm stores prior to overwintering. Consistent with the prediction of strategic advertisement, we show that male activity on extracts from females’ webs increased significantly 3 mo after the female first mated (typical length of the breeding season). Thus, these females had begun to add pheromone to their web again. At this time, 26% of these females re‐mated with a second male. If females re‐advertise receptivity to ensure adequate sperm stores, then we predicted a positive relationship between female reproductive output during the 3‐mo interval after copulation and the subsequent intensity of male response to web extracts. However, differences in male activity time were not related to the total number of spiderlings or the number of egg sacs a female had produced during the 3‐mo interval after the first copulation. This result could arise if male chemical manipulation of female receptivity decreases with time after copulation, or if the testing interval used in our study was too long to reveal variation in sperm depletion in females. Thus, although our results are consistent with the idea that females strategically alter pheromonal advertisement, we cannot distinguish this from the hypothesis that female receptivity arises from chemical manipulation by males.

A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism--the RAVE study

Widow spider-bite causes latrodectism and is associated with significant morbidity worldwide. Antivenom is given by both the intravenous (IV) and intramuscular (IM) routes and it is unclear which is more effective. To compare the effectiveness of IV vs. IM redback spider antivenom. Randomized controlled trial. Patients with latrodectism were given either IV or IM antivenom according to a randomized double-dummy, double-blind protocol. The first antivenom treatment was followed by another identical treatment after two hours if required. The primary outcome was a clinically significant reduction in pain two hours after the last treatment. A fully Bayesian analysis was used to estimate the probability of the desired treatment effect, predetermined as an absolute difference of 20%. We randomly allocated 126 patients to receive antivenom IV (64) and IM (62). After antivenom treatment pain improved in 40/64(62%) in the IV group vs. 33/62(53%) in the IM group (+9%; 95% Credible Interval [CrI]: -8% to +26%). The probability of a difference greater than zero (IV superior) was 85% but the probability of a difference >20% was only 10%. In 55 patients with systemic effects, these improved in 58% after IV antivenom vs. 65% after IM antivenom (-8%; 95% CrI: -32% to +17%). Twenty-four hours after antivenom pain had improved in 84% in the IV group vs. 71% in the IM group (+13%; 95% CrI: -2% to +27%). A meta-analysis including data from a previous trial found no difference in the primary outcome between IV and IM administration. The difference between IV and IM routes of administration of widow spider antivenom is, at best, small and does not justify routinely choosing one route over the other. Furthermore, antivenom may provide no benefit over placebo.

Sexual Cannibalism in the Brown Widow Spider (Latrodectus geometricus)

AbstractSexual cannibalism may represent an extreme form of male monogamy. According to this view, males gain reproductive success by sacrificing themselves to females. We studied the occurrence and timing of sexual cannibalism in the brown widow spiderLatrodectus geometricusand compared male courtship and mating behavior with virgin and with previously mated females.We found that events of sexual cannibalism are frequent, that they occur during copulation and that males initiate cannibalism by placing the abdomen in front of the female’s mouth‐parts during copulation (somersault behavior). Both the somersaults and mating occurred more frequently with virgins than with previously mated females. Our results support the hypothesis that sexual cannibalism is a male strategy in this species. The somersault behavior was previously known only from the redback spider,Latrodectus hasselti.It is as yet unknown whether self‐sacrifice has evolved more than once in this genus.

10 堺市内陸部におけるセアカゴケグモ駆除後の個体群動態(第62回日本衛生動物学会西日本支部大会講演要旨)

10 堺市内陸部におけるセアカゴケグモ駆除後の個体群動態(第62回日本衛生動物学会西日本支部大会講演要旨)

Safety of i.v. administration of redback spider antivenom

It is unclear what the risk of allergic reactions is with appropriately given dilute i.v. redback spider antivenom (RBSAV). Ninety-five i.v. administrations of RBSAV referred from January 2001 to November 2006 were reviewed. All patients had local pain, 72% radiating pain, 57% diaphoresis and 39% systemic effects. Four patients (4%) had immediate systemic hypersensitivity reactions: none were severe, one was moderate and three mild. In 32 patients followed up for 2 weeks, three (10%) developed serum sickness. RBSAV given i.v. had a low reaction rate.

Males assess chemical signals to discriminate just-mated females from virgins in redback spiders

In species where virgin females have higher reproductive value to males than nonvirgin females, selection will favour males that can discriminate female reproductive status. Similarly, while virgin females may actively seek to attract males, nonvirgin females may seek crypticity after mating if copulation is costly. Here we show that Australian redback spider males, Latrodectus hasselti, discriminate female maturity and mating status based exclusively on web-borne chemicals. Male activity on extracts from webs of virgin females significantly exceeded activity on extracts of webs of juveniles, nonvirgin females and solvent controls. While this level of discernment of female reproductive status has been found in other spiders, here we show that discrimination of web-bound chemicals produced by virgin females disappears rapidly after these females mate. Extracts of webs built by females immediately after copulation elicited no more interest from males than did solvent controls. Redback males dismantle much of their mate's web during courtship, and these results suggest that the web rebuilt by females after mating would not trigger male courtship. We speculate that this rapid shift would significantly reduce the opportunity for polyandry in nature.

A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom

There are no studies measuring antivenom concentrations following intramuscular administration. This study aimed to compare antivenom concentrations following intravenous and intramuscular administration of redback spider antivenom (RBSAV). Twenty patients recruited to a controlled trial comparing intramuscular and intravenous administration of antivenom had serial blood samples collected at 30 min intervals for 2 h after the administration of one or two doses of antivenom. Antivenom concentration was measured using an enzyme immunoassay. Ten patients received intramuscular antivenom but antivenom could not be detected in serum after either one or two vials, at any time point. The median time of the final sample after commencement of antivenom treatment in these patients was 3.2 h (1.8-5 h). Ten patients received intravenous antivenom (three one vial and seven two or more vials) and antivenom was detected in all patients. RBS AV given by the intramuscular route is unlikely to be effective in the treatment of redback (widow) spider bite.

Females reward courtship by competing males in a cannibalistic spider

Despite widespread recognition that intersexual interactions shape reproductive strategies, studies of male competition do not typically include effects imposed by females. In cannibalistic redback spiders, escalated fighting between rival suitors is predicted, as males are unlikely to mate with more than one female, and strong first-male sperm precedence favours mating with virgins. In staged competitions for matings between size mismatched rivals, smaller males adopted an alternative sneaking strategy. However, despite initial agonistic interactions, larger males did not pursue or incapacitate smaller males. When inter-male competition occurred, females struck at males frequently, although strikes were rarely seen when males courted in the absence of a rival. After minimal fighting, larger males engaged in significant courtship (3 h) rather than killing inferior rivals. Prolonged courtship was favoured by female behaviour, as males that attempted rapid copulation (smaller, sneaking males) were cannibalised before mating was completed. This premature cannibalism significantly decreases paternity in redback spiders. Thus, significant features of male competitive behaviour (i.e. prolonged courtship by larger males) may be predicted with consideration of the female’s response to male reproductive strategies. Although the effect of females may be more subtle in systems without the extreme reversed size-dimorphism of redbacks, these results suggest that female interests should be explicitly considered when studying inter-male interactions.

Route of administration of redback spider bite antivenom: Determining clinician beliefs to facilitate Bayesian analysis of a clinical trial

To determine current beliefs of Australasian emergency physicians, to form the basis of 'stopping rules' for a clinical trial of intravenous (i.v.) versus intramuscular (i.m.) redback spider antivenom. An email survey of fellows and trainees of the Australasian College for Emergency Medicine. There were 218 responses; 30% used the i.v. route exclusively, 16% used the i.m route exclusively, 17% used i.m. followed by i.v. if there was a poor initial clinical response, and 38% stated that they had no particular preference. The probability given by respondents that the i.v. route is superior allowed us to differentiate 'i.v. enthusiasts' from 'i.v. sceptics'. Median predicted response rates were 90% versus 80% for the i.v. route and 60% versus 75% for the i.m. route in the enthusiastic and sceptical groups, respectively. The median expected absolute advantage of i.v. compared with i.m. antivenom was 20% versus 5%, respectively. The median number-needed-to-treat threshold that would lead respondents to choose the i.v. route in preference to the i.m. was 5. Australasian emergency physicians have polarized views on the optimal route for administering redback spider antivenom. We were therefore able to define both sceptical and enthusiastic priors for a fully Bayesian trial analysis. Our findings support using a number needed to treat of 5 (20% absolute advantage) for powering a clinical study and for determining the point at which it should be stopped.

B12 大阪府におけるセアカゴケグモ生息密度と咬症例について(第59回日本衛生動物学会大会特集)

B12 大阪府におけるセアカゴケグモ生息密度と咬症例について(第59回日本衛生動物学会大会特集)

B11 セアカゴケグモ分布の現状(第59回日本衛生動物学会大会特集)

B11 セアカゴケグモ分布の現状(第59回日本衛生動物学会大会特集)