{"id":10794,"date":"2019-07-24T09:31:44","date_gmt":"2019-07-24T14:31:44","guid":{"rendered":"https:\/\/uwm.edu\/field-station\/?p=10794"},"modified":"2024-08-26T15:40:34","modified_gmt":"2024-08-26T20:40:34","slug":"tree-crab-spider","status":"publish","type":"post","link":"https:\/\/uwm.edu\/field-station\/bug-of-the-week\/tree-crab-spider\/","title":{"rendered":"Tree Crab Spider"},"content":{"rendered":"\n

Howdy, BugFans,<\/p>\n\n\n\n

The BugLady was checking around the edge of a gravel parking lot near the Ozaukee Washington Land Trust\u2019s Lake Twelve property (because there are bugs there, too) when she found this beauty (it took two trips and two different cameras to get a few almost-in-focus shots \u2013 sometimes it\u2019s like that).<\/p>\n\n\n\n

She had two immediate reactions: 1) what is<\/em> it? And 2) it looks like an octopus clinging to a reef!<\/p>\n\n\n\n

It\u2019s a crab spider in the tree crab spider genus Tmarus<\/em>, probably Tmarus angulatus<\/em> (thanks, as always, to BugFan Mike). Mike says that there are a few documented records of this species in Wisconsin, but they are probably more common, it\u2019s just that we don\u2019t typically hunt for spiders in trees. And, of course, they seem to have the \u201ccamouflage\u201d thing figured out.<\/p>\n\n\n\n

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Crab spiders (family Thomisidae), best known for the species that ambush insects on flower tops, are long-time favorites<\/a> of the BugLady. They get their name from their tendency to hold those four, extra-long front legs in a crab-like pose and for their tendency to move sideways. Crab spiders don\u2019t spin trap webs to catch their prey, they ambush it on the hoof. They paralyze their prey and then introduce (bugguide.net<\/a> says \u201cvomit<\/em>\u201d) digestive enzymes into it, wait for its innards to soften, suck out the tenderized tissue, and throw away the empty.<\/p>\n\n\n\n

They do spin silk, protecting themselves from a fall by playing out a drop line as they hunt, and this Tmarus<\/em> spider was guarding her eggs in a chamber she created by bending and webbing together a slender day lily leaf. She will stay nearby for about a month to protect her eggs from predators.<\/p>\n\n\n\n

About the genus Tmarus<\/em> the BugLady could find very little. The spiders appear regularly on state biodiversity lists, and there are a bunch of scholarly articles about new species being discovered in different countries around the world (one article from Sri Lanka was titled \u201cTwigs that are not Twigs<\/em>\u201d). The BugLady was gratified to find that the spectacular Tmarus marmoreus<\/em> spider in Australia is, indeed, nicknamed the Octopus spider<\/a>. It hunts by dangling from a line of silk with its front legs poised and ready.<\/p>\n\n\n\n

Their knobby bodies are usually well-camouflaged on bark and other vegetation, where they look like buds or broken twigs. The Field Guide to the Spiders of California and the Pacific Coast States<\/em> tells us that with \u201cforelegs along either side of a stem, they wait for an insect to wander between them.<\/em>\u201d According to the Kansas School Emporium\u2019s Checklist of Kansas Crab Spiders<\/em>, Tmarus spiders have been observed eating ants, which most spiders avoid.<\/p>\n\n\n\n

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Tmarus angulatus<\/em>, sometimes called the Tuberculated crab spider, is small spider with a body about a half-inch long (females are larger than males) that is found across the US and southern Canada. Some are pale and some were dark, and the BugLady saw a picture of a gravid female with a dark cephalothorax (front end) and a pale abdomen, with a caption that said that she looked like a spittlebug nest. Well, maybe. Here\u2019s a little gallery of shots of Tmarus angulatus<\/em> :<\/p>\n\n\n\n