Tales from the woodpile #7

NOT FOR ARACHNOPHOBES

Cutting up wood last we week came across this white disc (see picture left) attached to the wood deep in one of the splits in the trunk. The owner of the disc soon revealed itself – a Social Huntsman (Delena cancerides) – which wasn’t acting too socially. After a few aggressive moves it settled down over its possession so I could easily observe it.

Spiders are different from insects in obvious ways. An insect has three body parts (head, thorax and abdomen), antennae, compound eyes and six legs. Spiders have only two body parts – a cephalothorax, from the Greek words cephalo meaning head and thorax meaning trunk or chest, and an abdomen. The cephalothorax has no antennae but has attached eight legs (see picture right). The knees of a huntsman instead of flexing vertically like most arthropods, flex forward. This allows the spider to be able to sidle into narrow spaces. The cephalothorax also houses eight simple eyes under which are two black chelicerae which contain the fangs. Huntsman poison is not regarded as fatal for humans.

Outside the chelicerae, looking like a pair of small legs are the palps (or pedipalps). Palps contain chemical detectors that function like smell or taste organs. In male Huntsmans the palp is also used for mating. In the final segment of the palp there is a structure that siphons up sperm packets from the male’s abdomen. The palps are then used to transfer the sperm packets to the female during mating. Once fertilised, the female produces a silk sac into which it lays up to 200 eggs, which is where this blog began (see picture above left).

This is not palp fiction. This is for real.