Flower crab spider (Misumena vatia)

Dear Readers, I was so intrigued by this bright yellow spider yesterday that I thought I’d do some research. It’s known that the females of this species can change their colour from white to yellow (and indeed in North America this species is known as the goldenrod spider, as that’s the plant that it’s most frequently found upon). However, the change takes a full 25 days to occur, which doesn’t sound especially helpful if you’re doing it for camouflage. Furthermore, it appears that the spider’s ability to catch prey doesn’t decrease if it’s not on a ‘matching’ flower – let’s not forget that insects see colour differently from mammals, with UV light playing a big part in perception, and so a colour difference that is very apparent to us may not be so clear to an incoming hoverfly. 

White form of Flower Crab Spider (Photo by By Charles J. Sharp – Own work, from Sharp Photography, sharpphotography.co.uk, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=81672235)

I am indebted to Tone Killick, one of the administrators of the UK Spider Identification Facebook page, who produced a very interesting paper on this fascinating spider. He is unconvinced about the possibility that the change in colour is to evade predators – this is a very speedy spider, and furthermore birds are able to spot the arachnid even if it’s perfectly matched to its flower. And we already know that it doesn’t apparently help the spider to catch prey. The spider has a very low rate of success (apparently it only catches 3.5% of the prey that it attempts to grab in its spikey front legs), which means that it has to wait around on a flower for a very, very long time before it gets a meal. And here’s where Killick makes an interesting lateral link. The yellow pigmentation is caused by a chemical called ommochrome, which has been shown to provide protection against UV damage in spider’s eyes. Could it be that, if a spider spends a long time in sunshine, she develops the yellow colouration as a sun screen (we could hypothesise that spiders that stay white live in shadier places). Clearly more research is needed, but for now let’s move on to the other interesting facet of the spider’s life, reproduction.

All of these biggish yellow and white spiders are female. The males are only 3-4 mm long, while the females are 9-11mm. Furthermore, the males look completely different.

Male Flower Crab Spider (Photo by By James Lindsey at Ecology of Commanster, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1669767)

In the spring, the tiny males run through the flowers following the silken threads that the females leave as they move from one bloom to another. Upon finding a female, they scramble onto her abdomen while the female continues to go about her business, seemingly oblivious.

Female eating fly with male on her abdomen (Photo by S Drozd Lund from Misumena vatia photo – image 105272 (biopix.com))

The male then taps on the female to see if she’s receptive to some sperm transfer (like you do) and if all goes well, they mate. The male then makes an extremely speedy retreat, before he ends up as dinner. He must keep all eight legs crossed that the female hasn’t already copulated, as if so she can be extremely (life-threateningly) grumpy.

The female lays 150-400 eggs on a suitable leaf and covers it with lots of silk. Then she starts her guard duties – during this time, the only way she will eat is if a particularly silly fly blunders into her space and she can grab it. After 25 days the spiderlings hatch, and many will fly away by standing on some vegetation and holding a strand of silk which will act as a parachute. Alas, many dangers await these tiny spiders, though they can survive the freezing temperatures at 5 km above the earth’s surface. Many will be eaten by predators, and others will end up in an unsuitable environment. Some, however, will survive to adulthood, to delight amateur arachnologists and lovers of the unexpected everywhere.