11-Apr London’s Tiny Titans

By water there may be swarms of insects, some of which may bite and others that follow you as you walk by. These are often non-biting midges Chironomidae. As they hatch they tend to cause some disturbance on the water surface which can be responsible for the first significant ‘rise’ of fish. Anglers can them buzzers. Swarms of alderflies have the habit of flying gently upstream by rivers, such as the river Wey. If the swarming insects have long, dangling legs they may even be dance flies Empididae. Some have prominent snouts and others have distinctive, upturned abdomens.

Two insects very much associated with April are the St Mark’s fly Bibio marci and the insect inside cuckoo spit Philaenus spumarius. The St. Mark’s fly owes its name to its first appearance being traditionally on or around St Mark’s Day, April 25th. It is about the size of a small blow fly, but thinner and more hairy. It carries its long legs in a bundle dangling below its body as it flies These are males waiting for the females who are usually sat on the grass nearby. Once the females take flight, the males then pounce on them, mating in mid air. Cuckoo spit is the name given to the pockets of white froth we see at this time of year on leaves and stems.

The insect involved is a froghopper or spittlebug. The froth is exuded by its nymphs expelling air through a sticky secretion on their abdomens. It is thought to have two functions i.e. protecting against desiccation and hiding the nymphs from predators.

There is also a lot more evidence of caterpillar activity this month, with many more holes appearing in leaves; the caterpillars themselves are more difficult to find although not for nesting tits which are known to collect up to five hundred a day to feed their young. It is well worth visiting commons this month with a range of different habitats such as Wimbledon and Mitcham commons, both of which are well-known for their insect diversity. More unusual insects that might be seen in more unusual situations could include the impressive Bloody-nosed beetles on patches of Lady’s bedstraw, flea beetle damage on seedlings, whirligig beetles careering around the surface of ponds, owl midges attracted to wild arum lilies, sawflies hanging around plants they intend to parasitise, fungus gnats either feeding or laying their eggs on fungi and perhaps your first hoverfly or cranefly. By the end of April all this insect activity means we start to notice a lot more damage to the leaves of garden plants and crops. This is because the leaves are not just being eaten or pierced to suck sap but species such as sawflies are busily laying eggs in them.

Another distinctive insect seen this month is the bee fly Bombylius spp. Their high-pitched whining buzz is noticed first, before they dart away. They are nectar feeders, with a penchant for yellow flowers. They fire their eggs towards bare ground, near the nesting holes of bees. When their eggs hatch, their larvae then invade the burrows stealing their contents and possibly eating the bee larvae. It is their long projecting proboscis, bulging eyes and ability to hover that tends to attract attention.

Although there are over forty different ladybirds in London there are only around twelve which have spots noticeable enough to attempt identification by counting them. Another four or five can be identified by their colours or other distinctive markings. Those most commonly encountered are the 2, 7, 10, 14 and 22 spot ladybirds as well as the Orange ladybird which usually has 16 spots. Variation, especially in the last species, can cause problems in making an accurate identification. Probably the 7, 14, 16 and 22 spot are the easiest to recognise.

The 7 spot fortunately has 7 spots but these can either be red or black on a black or yellow background. The 14 spot is yellow but can have between 4 to 14 black spots and the 16 spot as mentioned is orange with between 12 and 16 spots. The latter ladybird is often associated with ash, oak or sycamore trees. The 22 spot is yellow and has a narrower range of black spots, just between 20 and 22.

The Harlequin ladybird is the villain of the piece. It only arrived in 2004 but has been out-competing our native ladybirds with its wider diet and longer breeding period. It even eats the larvae of other ladybirds. It is also larger, being generally over 5 mm. in length and often has a noticeable keel around the edges of its wing cases. This helps a little to identify it but unfortunately it can be black or orange and also have red or black spots. Not only that but there are over a hundred other different forms.

It is the 2 spot we generally see the most of. It can be red or black with either 2, 4 or 6 spots. Usually it only has 2 when we see it around our window frames during the winter. As a general rule we tend to notice ladybirds on roses or other garden plants with infestations of aphids but conifers and low growing vegetation in meadows are also good places to look for them.

Tube webs get noticed covering holes in old walls and also on bushes. Sometimes they have a central hole with radiating lines of silk which act as trip wires for unsuspecting insects as is the case with the Snake-back spider Segestria senoculata. When the web is more sock-shaped it could belong to the Purse-web spider Atypus affinis which particularly likes to live on the south-facing sides of ant hills. Where the webs are hammock-shaped, the spider often hangs underneath, biting its prey through the silk then dragging it through and then repairing the hole later. There are many other shapes of web, some are tent-shaped and others like inverted cups, or perhaps covering a whole flower head or just encasing a cocoon of eggs. If a random web is seem with lots of criss-crosses of silk this could indicate the work of a comb footed spider (Theridiidae) and an excessively flimsy affair which is almost invisible could belong to the Daddy long-legs spider Pholcus phalangiodes.

Similarly, one full of spiderlings is typical of the Nursery web spider Pisaura mirabilis. Unfortunately, there are hundreds of different spiders and identifying them accurately is not an easy task. Those mentioned here are just some common and widespread species in London but even so they may well not be seen until later in the year. To encourage spiders to show themselves you can touch the web gently with the tip of a grass leaf which sometimes draws them out. In the past they used tuning forks for the same purpose as spiders are so sensitive to vibration. Although not expected outside harvest time, you may well see your first harvestman (Opiliones) this month. These close relations of spiders have outrageously long legs and usually just two eyes set rather comically on a bump on their backs.

Mites

Mites (Acari) are another close relation of spiders which may also be seen this month as some are at last coming out of hibernation. Most are not noticed due to their small size (usually less than 2mm) and dull colours. However, there are exceptions such as the vivid scarlet species that used to be described as “red bags with legs”. They are often seen after soil has been disturbed or occasionally after rain. If they are slightly bigger, perhaps 4 mm, and seem to be covered in a red fur they could even be velvet mites and these most always get noticed.

Mites are thought to be one of the most common group of invertebrates in the soil not only in numbers of individuals but also in the number of species. It has been estimated that in some areas of grassland there could be as many as 500 million/acre. Their important role in decay, as many feed on decaying organic matter and associated fungi as well as bacteria, cannot be underestimated. Yet we still know so little about them and even less of their autecology. Another reason that they tend to get ignored is that some live quite deep in the soil, perhaps as much as a metre down. These subterranean species tend to be even smaller, weaker, less pigmented and less armoured than the ones we see at the surface.