The biology of New Zealand and Queensland pirate spiders (Araneae, Mimetidae): aggressive mimicry, araneophagy and prey specialization

Abstract

Mimetus sp. indet. and Mimetus maculosus, from New Zealand and Australia, respectively, were studied in the laboratory and in nature. Behaviourally, the two species were very similar. Each was found to be primarily an araneophagic spider which invaded alien webs, acted as an aggressive mimic by performing a variety of vibratory behaviours to which the prey‐spider responded as it normally would to its own prey, and attacked by lunging at close range, subduing its victim with a strong, apparently spider‐specific venom while holding the spider in a ‘basket’ formed by its spine‐covered legs. In nature, these mimetids were observed to feed on a restricted range of spiders: orb web‐building araneids and space web‐building theridiids. Sometimes, they occupied other types of webs, but in the laboratory they captured only araneids and theridiids efficiently. They captured non‐cribellate amaurobiids considerably less efficiently, and never captured other types of spiders. Occasionally, the mimetids fed on insects ensnared in araneid and theridiid webs and on eggs of theridiids. Experimental evidence indicated that vision was of little or no importance in the predatory behaviour of these mimetids. The behaviour of the mimetids is compared to that of Portia, an araneophagic web‐invading salticid, and the results of this study are discussed in relation to hypotheses concerning salticid evolution.