Spider Sunday: Cross Spider

The pretty famous cross spider (Araneus diadematus) is the spider for today. This orb-weaver spider is often seen in autumn, but the spiderlings can be spotted in the spring season. Unlike the nursery web spider, the cross spider does not care for the spiderlings. A female will lay eggs, spin a cocoon and protect it, but dies late in the autumn season. The eggs hibernate during winter and hatch the following spring. The first few days, the spiderlings stay close to each other in a bundle. They are bright yellow with a dark patch on the abdomen and because they bundle up, you can easily spot them. If disturbed, they will disperse, but once the danger is over, they group themselves again. After their first moult they fly away where the wind takes them and live independent lives. Cross spiders aren’t shy, so as they get bigger, you can see them more and more around gardens. Everyday they will make a fairly large web, which can be annoying if you walk through them 😉

The most conspicuous feature of the cross spider is the cross-like marking on its back. This marking is not due to a colouration of the skin itself, but is a byproduct of the metabolism. A side effect of digesting insects rich in protein is that ammonium is produced. This is a toxic substance. Humans (and various animals) have a liver and kidneys to deal with that and secrete it as urine or faeces. Spiders however, only have specialised gut organs that convert ammonium into guanine. Instead of pooping it all out, most guanine crystals are collected in specialised cells on the back just under the skin. Because the crystals reflect light, they look brighter than the surrounding cells. In the cross spider, these specialised cells just happen to be arranged in clumps that form a cross-like shape. Later in the year, spiders tend to secrete more guanine and in doing so lose colour, making the cross marking less visible. The other markings on the back may resemble a crown and that is the reason for its latin name ‘diadesmatus’.

All pictures were taken in 2016, between May and July.



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