I want to start off this post with announcement: Our Wild World will be switching to one post a week, on Wednesdays, instead of posts on Wednesdays and Sundays. Things have just gotten too busy for me to keep up with posts twice a week. This was originally supposed to be a weekly blog anyway, so things are just changing to how they were meant to be.
Now that that’s out of the way, we can talk about today’s animal, the goldenrod crab spider. Goldenrod crab spiders are found in the northern hemisphere, in North America and Europe. They are found on fences, leaves, and are especially fond of flowers.
Goldenrod spiders are the largest crab spider in North America, with females growing to be 10mm excluding their legs, and males reaching 5mm. Crab spiders are named because they somewhat resemble crabs, with wide, flat bodies and long front legs that are held open.
Goldenrod spiders vary in colour, depending on where they live. You see, crab spiders are ambush predators, waiting on flowers for prey to come swooping by. When an unfortunate insect chances by, the spider grabs their victim with their front legs, and then injects venom into the insect. They feed mainly on flies, butterflies, grasshoppers and bees.
Though goldenrod spiders hang out on lots of different types of flowers, the ones they most favour are goldenrods (no surprise there), trillium, and white fleabane. To camouflage themselves, goldenrod spiders are either bright yellow or white, sometimes with dark markings on the abdomen.
The spiders can change between the two colours, switching between yellow and white depending on the type of flower they are on. They switch colours by secreting a yellow pigment into the body, and excreting the pigment when they want to go from yellow to white. Once the pigment has been jettisoned, however, the spiders have to remake the yellow pigment, so it takes longer to transition from white to yellow (10-25 days) than from yellow to white (6 days). The spiders change colours based on what they see, as crab spiders who have had their eyes painted do not change colour to reflect the colour of flower they are on.
Crab spiders rely on their expert camouflage not only to catch prey, but also to avoid becoming prey themselves. Because they don’t try and actively avoid predators, crab spiders can focus on growing and reproducing. That’s why female crab spiders have such huge abdomens — and there is a direct correlation between female weight and egg clutch size, so bigger females do better reproductively.
I’m not a huge fan of spiders, and I have a lovely memory of a crab spider parking itself on my shirt when I was a child (it was a flowery shirt). But crab spiders as whole aren’t too bad. At least they are pretty colours and don’t looks as terrifying as some species of spider.