A common behavior exhibited by protostomes in response to danger is adopting a threatening posture. When, for example, a specimen of Brachypelma smithi (mygalomorph spider) is threatened outside its burrow, it reacts by making itself appear larger by shifting weight onto the rear legs while simultaneously raising the front legs and exposing the fangs. Another physical defense mechanism of many species of my-
galomorphs is that they use the fine sharp hairs that cover them to pierce their predators. This is not only painful, but may be toxic (these hairs can pierce human skin to a depth of 0.078 in [2 mm]). A spider can release these hairs by rubbing the hind legs against the abdomen. In addition to making themselves appear larger and covered with sharp and, in some cases, toxic hairs, they can also squirt a liquid from their anus.
A novel form of defensive behavior in spiders is found in females and immature males of the black widow (Latrodectus hesperus). When threatened, the black widow emits strands of silk and manipulates the silk to cover its vulnerable abdomen and, sometimes, the aggressor. Especially interesting is the defensive behavior of the cerambycid beetles (genus Ham-maticherus) that use spine-like appendages on their antennae to whip their aggressor. Equally fascinating is the behavior of arctiid moths that produce a series of clicks when detecting the sound made by hunting bats.
A well-known active defense system is found in social insects such as honey bees, termites, and ants. The latter two organisms actually maintain a caste of "soldiers" for colony defense, as do several species of aphids (Colophina clematis, C. monstrifica, C. arma). When threatened, these organisms attack by injecting venom into the aggressor and can use their powerful mandibles to incapacitate. In aquatic organisms such as those found in the order Decapoda, cuttlefish and squid defend themselves not only by an ability to escape, but also by discharging ink that temporarily disorientates the aggressor. Some decapods in the order Octopoda, which includes the octopus, have a similar ink defense system. At least one case has been observed in which Octopus vulgaris was recorded actually holding stones in its tentacles as a defensive shield against a moray eel.
In general, organisms during early ontogenetic development approach low-intensity stimulation and withdraw from high-intensity stimulation. Protostomes can always escape high-intensity stimulation offered by an aggressor by crawling, swimming, flying, or jumping. Such behavior is easily observed in grasshoppers and the decapod Onychoteuthis, popularly known as the "flying squid." The flying squid can escape aggressors by emitting strong water bursts from its mantle to propel the animal into the air where finlike structures allow it to glide for a brief period of time. Fleeing is not always effective. The katydid, Ancistrocerus infictus, does not confront aggressors by an active defense system such as that found in spiders, ants, honey bees, and termites. Rather, Ancistrocerus may be found living near the nests of several wasp species. It is these wasps that provide protection for the katydid.
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