The Entomologist’s Year: What To Look For In Spring (Part 2).

April Flies

For me, one of the star attractions of April is the Dark-edged Bee Fly, Bombylius major. Seeing the first one in the garden on a warm sunny day is a sure sign that spring is really here, even if it snows the very next day! These are lovely flies to watch as they hover at a flower supping nectar through their long proboscis. They readily settle when the dark front edge of the wing that gives them their common name can be seen. 

There are nine species of bee fly in the UK but only Bombylius major is common and widespread. All of them are parasitic on solitary bees and wasps (hymenoptera). Female Bombylius major have a fairly scatter-gun approach to egg-laying. A suitable sandy spot is located, presumably with nesting bees, and the female dips the tip of her abdomen into the soil to pick up minute particles. These coat her eggs, adding weight to them and she then hovers and flicks her abdomen, firing out a barrage of eggs. The larva hatches out and crawls the short distance into the nest and finds an open chamber. It then becomes inactive, waiting for the bee larva to become fully grown whereupon it becomes an ectoparasite, attaching to its host and sucking out its bodily fluids.

Other interesting spring flies to look out for include the Myopa species, the so-called ‘bee-grabers’. These are members of the Conopidae family (known as thick-headed flies) and they too are parasites on various species of hymenoptera (seems to be a theme here…). Unlike the cuddly looking bee fly, these flies look rather sinister, especially when they sit about twisting their head this way and that as they scan anything that comes near them, looking for a suitable host or mate. Rather than randomly firing eggs towards a bee’s nest, these flies will actually jump onto a passing bee and then lay an egg into its abdomen which becomes an internal parasite.

Two other ‘nice’ flies to look out for at this time of year are Gonia picea and Tachina ursina. These are both members of the Tachinidae, another group of parasitic flies, whose larvae develop mostly in moth caterpillars but also those of butterflies and sawflies. I usually make a trip to the Norfolk Brecks this time of year specifically to find these two flies. Gonia isn’t the most attractive looking species but has a certain charm while Tachina ursina definitely wins in the fluffy cuddliness stakes.

Green Tigers and Fencepost Jumpers

A visit to heathland in spring often turns up one of my favourite beetles, the Green Tiger Beetle Cicindela campestris. This is a beautiful creature, iridescent green with yellow spots on the wing cases. Its long legs have a purple sheen to them and it actively runs around on warm days hunting for prey and snapping it up with its powerful jaws. It is an altogether impressive looking and rather formidable beast. The larva lives in the bottom of a funnel-shaped pit with its massive jaws protruding, waiting to grab and eat anything that tumbles in to its pitfall trap of a lair. A little parasitic wasp (Methocha articulata) takes advantage of the situation by luring the larva out and then paralysing it with a quick sting as it grabs her. The wasp then walls the poor beetle larva up in its own home, depositing an egg in there so that her larva has a well stocked refuge to develop in.

A spring visit to the Brecks would be incomplete without finding a Fence Post Jumping Spider, Marpissa muscosa. This impressive spider is a relative newcomer to Norfolk and is largely restricted to the south east of England. These beautifully marked spiders favour sunlit fences and trees. When a male approaches a female he holds his thickened front legs up and waves at her as part of his courtship display. The enlarged palps are used to transfer a sperm package to her epigyne – if she approves of him of course!

Mining Bees

April is a good time to look out for solitary bees, especially the Andrena or Mining Bees. You will soon discover that there is a bewildering array of species, many of which (especially the males) all look rather similar. There are in fact 67 species of Andrena in the UK with around 45 in Norfolk, many of which are on the wing at this time of year. 

Although some only take pollen from a particular source (e.g. sallows) many utilise a variety of flowers and will also favour the same habitats for nesting so it is easy to find several species together. Tree blossom is often favoured so check out Blackthorn blossoms and any fruit trees (e.g. apple, plum). In urban settings Cherry Laurel can be very productive and don’t forget Dandelions and Red Deadnettles for these ‘weeds’ are important sources of nectar as well as pollen.

Spring Butterflies

April sees Garlic Mustard sprouting up in the hedgerows. As their first flower buds begin to open, it is sure sign that Orange-tip butterflies will be on the wing for this often under-valued wayside flower is one of the principle foodplants for their caterpillars (the other is Cuckoo Flower or Lady’s Smock). The female Orange-tip usually lays just a single orange egg on each suitable food plant she comes across. This is because her caterpillars become cannibals if the food plant runs out, eating their own siblings.

Only the male butterfly has the characteristic orange tips to the forewings but both sexes have lovely greenish mottling on the underside of the hindwings, rather poetically described by Jeremy Thomas as being mossed.

Other butterflies now appearing include the Holly Blue and the Speckled Wood. The Holly Blue goes through boom and bust years, depending on how much it is affected by a tiny parasitic wasp (Listrodromus nycthemerus). As the butterfly population builds up, so does that of the parasite until butterfly numbers crash along with the wasp then the cycle starts all over again. The butterfly has two broods a year. In spring eggs are laid most often on the buds of Holly while in summer Ivy is the predominant choice.

The Speckled Wood is a butterfly of dappled shade where its pattern of pale yellow on a dark brown background gives surprisingly good camouflage. Many is the time I’ve gone out looking to photograph my first of the year and only noticed one when it has flown up from practically under my feet. It is one of the few UK species that has actually increased in number and distribution over recent years, following on from a huge population crash in the mid 1800s when it was lost from large parts of the country. Ironically it has benefitted from the poor management of our woodlands that led to the decline of other species, notably some of the fritillaries. As coppicing was abandoned and the woodland canopy closed over, the Speckled Wood increased. It has several overlapping broods a year which also helps. Climate change has also played a part with milder springs and winters. Butterflies, like so many of our invertebrates, have a complex array of requirements in order to thrive, many of which are poorly understood or even recognised.

‘E is for Emperors’

Staying with Lepidoptera, a visit to local heathland may bring a glimpse of an Emperor Moth, seen as an orangey blur hurtling along at a rate of knots, rather like a Small Tortoiseshell butterfly on speed. This will be a male in search of a newly emerged virgin female to mate with. The females give off a powerful scent to attract the males whose large feathered antennae allow them to pick up their presence from over a considerable distance. Artificial pheromone lures are now available to attract these magnificent moths.

‘D is for Dragons and Damsels’

And finally, the first Large Red Damselflies of the year should be emerging from my garden pond by the end of the month. As soon as their wings are stiff enough to fly, they leave the pond plants on which they emerged and settle into the nearby shrubs to fully harden off, away from the predating beaks of the resident House Sparrows.