Mimetidae, pirate spiders

Mimetidae, pirate spiders overview

Mimetidae, the pirate spiders, get their common name from their behaviour of invading the web of a spider of similar size, killing the spider who built the web and taking it over. They way they do this is to pretend to be either a prospective mate or prey. So they pluck and move strands of silk on the web, and when the spider who built the web comes to investigate they attack, paralyse the spider and eat it by sucking its liquefied body contents out through a hole it has made, usually in one of the legs.

When it comes time for the female to lay her eggs sac she attaches the sac to a structure by spinning a wiry thread as a stalk. This wiry thread is also spun around the egg sac giving it some protection. Then she goes off and leaves the sac hanging off by a stalk. She never returns and does nothing more to protect her young. You can see a photograph of an egg sac below. When the spiderlings hatch out they climb up the stalk and start their life of piracy.

There are just four species in Britain and only two in Scotland. All are small with a body size of 2 - 4 mm. The abdomen in usually patterned and has raised protuberances or tubercles on the dorsal surface. The legs are usually long, striped and spiny. Males and females are similar.

Ero cambridgei or E. furcata

Mimitidae egg sac, pirate spider egg sac

Above is the eggs sac of either Ero cambridgei or E. furcata. I am not sure which because both are very similar and both are found in north east Scotland and the whole island of Great Britain. This one was found hanging from the inside of the lid to my compost bin. The stalk is clearly seen as well as the wiry silk used to wrap around the egg sac. Below you can see a close up of the silk and the sac itself which is of a lighter colour.

Mimetidae egg sac close up, Ero egg sac close up

Below is one of the spiderlings that emerged from the top of the egg sac, perhaps the wiry silk is too tough to cut through.

Ero cambridgei or Ero furcata, priate spider spiderling

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