Here is my second gallery of little creatures, not insects this time (they are here) but arachnids. No need to worry, though – they are tiny, so small they are completely harmless to us as well as almost invisible.
Spiders are more like us than like insects in that they don’t change their form as they grow: they are already recognisably spiders when they hatch from their eggs, and they simply get bigger. However, they have rigid exoskeletons like insects, so they can only get bigger by moulting, and some species change colour as they mature.
The familiar St Andrew’s Cross spider changes colour significantly. The 2mm individual above is the greyish-brown of newly-hatched spiderlings but (if she survives) will turn orange-brown with similar coloured stripes, then the stripes will become more distinct, and finally her background colour will darken. Here is an adult.
Some species of spiders just never grow very big, and these two are good examples. The second lives amongst us (if you’ve noticed a wisp of silk in a tiny groove or hollow on your walls or a cupboard shelf, there may well of have been one of these behind it) and has therefore acquired a common name. The first, however, is one of many species living anonymously in our gardens. Saying it is in the ‘Anelosimus group’, as my friendly spider expert did, is about as precise as saying ‘some kind of dog’. It is often the best we can do, however, since so many tiny critters remain scientifically unknown and un-named.
Deciding whether a particular spider is an adult or not can be problematic unless we recognise the species and know how big they usually grow. In this case, I don’t really know but I’m pretty sure that this is nearly as big as it gets because I would have noticed them in my garden long ago if they grew much bigger. After all, I know the Lynx (pretty photo), Flower Spiders (lots of photos) and Jumping Spiders (lots of photos) well enough, and they are all usually under 8mm.
Male spiders of most species are smaller than the females, often a lot smaller. This little bloke is the male of the common spiky black and white Jewel Spider or Christmas Spider. He is about 2mm square, while she is about 8mm. Other examples of this size difference (aka sexual dimorphism): Flower spider and Golden Orb-weaver.
If you see a tiny spider in the web of a much larger one, it isn’t always a male of the same species. Dewdrop spiders, for instance, are tolerated in webs of larger orb-weavers (Neoscona sp., about 8mm, is in the background here but St Andrew’s Cross and even the enormous Golden Orb-weaver are known hosts), living on scraps and maybe accidentally-caught tiny prey.
Lynne Kelly has said, in Spiders – Learning to Love Them, that wherever we are in the world there is likely to be a spider within a metre of us. I’m sure she’s right, but would add that the reason we are not constantly aware of them is that most of them are so small.