Bee-flies are a widespread group of insects in the Bombyliidae family. There are over 4,500 species found worldwide, with around 40 species native to the UK. Bee-flies get their name from their superficial resemblance to bumblebees, having a furry thorax and abdomen and wings that buzz loudly during flight. However, they can be distinguished from bees and wasps by having a long proboscis that curls under their head when not in use.
Bee-flies found in the UK can be divided into three main groups:
Long-proboscid bee-flies
These bee-flies have an exceptionally long proboscis that can be over 10mm in length. There are four species found in the UK:
– The dark-edged beefly (Bombylius major) – The most common and widespread long-proboscid bee-fly in the UK. It has a brown furry body with patterned wings.
– The dotted beefly (Bombylius discolor) – Similar to the dark-edged beefly but with pale spotting on the wings. Less common than B. major.
– The dusky beefly (Bombylius ater) – A relatively rare species associated with woodland. It has an all black appearance.
– The large beefly (Bombylius medius) – Our largest bee-fly species, found locally on chalk downland and coastal areas.
These long-tongued beeflies use their long proboscis to reach nectar in flowers with deep corollas, especially plants in the Fabaceae family like vetches and clovers. The dark-edged bee-fly is sometimes known as the ‘humble-bee fly’ for its resemblance to bumblebees feeding on flowers.
Short-proboscid bee-flies
These species have a much shorter proboscis under 6mm in length. There are around six species found in Britain including:
– The common bee-fly (Bombylius minor) – One of the most frequently encountered bee-flies across the UK. It has an all black appearance with a grayish furry thorax. It flies early in the spring, even in cooler weather.
– Geron’s bee-fly (Bombylius geron) – A small black bee-fly with a red furry thorax. It has a mainly southern distribution in England and Wales.
– The stripe-headed beefly (Bombylius discolor) – Distinctive yellow and black striped head. Widespread but locally distributed.
– Scaeva species – These are medium-sized bee-flies with patterned or banded abdomens. There are several similar looking species that are hard to distinguish.
The short proboscis means these species favor flowers with open, shallow corollas like members of the Apiaceae family. They emerge slightly later than long-proboscid bee-flies, typically flying in mid to late spring.
Parasitic bee-flies
Some bee-flies are parasites of solitary bees during their larval stages. Two species found in Britain fall into this group:
– The brown-banded carder bee parasite (Thyridanthrax fenestratus)
– The red-legged beefly (Bombylius fulvescens)
The larvae of these parasites live in the nests of bees like mason bees and leafcutter bees, feeding on the pollen left for the host larvae. As adults the flies feed on nectar from various flowers. They can be observed flying low over the ground in early spring seeking out host nest sites.
Life Cycle
All bee-flies have a complete metamorphosis with distinct egg, larva, pupa and adult stages. The details of their life cycle can vary depending on the species.
Eggs
– The adult female bee-fly lays batches of small white eggs, usually on or near the host food source, e.g. on flowers for nectar-feeding adults or near bee nests for parasitic larvae.
– Species like Bombylius major lay eggs while hovering in flight over flowers using their long ovipositor. Up to 100 eggs may be laid by a single female.
– Egg-laying occurs in spring, usually April or May in the UK. The eggs hatch after around 5-7 days.
Larvae
– The legless larvae are cream or yellowish and worm-like in shape, tapering towards the rear end. They may reach 10-12mm in length when fully grown.
– Larvae of the non-parasitic beeflies feed on pollen stores inside flowers. Species with very long proboscises lay eggs deep inside flowers where larvae can feed.
– Parasitic larvae consume pollen left as food inside the nests of host bees. They moult through three larval instars over 4-6 weeks to complete their development.
Pupae
– The pupae are formed inside hardened last larval skins. This takes place in the soil for non-parasitic species.
– Parasitic beeflies pupate inside the host nest. The parasites complete their life cycle rapidly so they emerge just before or at the same time as the adult host bees.
– Pupation lasts 2-3 weeks before the adult beeflies emerge. This typically occurs in July or August.
Adults
– The adult bee-flies feed on nectar from flowers through the summer after emerging from pupation. Some species may live for several months.
– Mating takes place on the wing. Males patrol circuits in search of females and mate after aerial encounters.
– Adults enter diapause during the winter, often sheltering in crevices like holes in trees or walls. They re-emerge early the next spring to mate and begin the life cycle again.
Habitats
Different bee-fly species inhabit a variety of habitats across the UK:
Woodlands
Ancient, undisturbed woodlands provide habitat for some of the rarer beefly species:
– The dusky bee-fly is associated with old woodlands, particularly ancient beech forests.
– The large bee-fly prefers woodland clearings and rides on calcareous soils.
Dead wood and tree holes provide winter shelter for adults. Main food plants include early flowering trees like sallow and blackthorn.
Grasslands
Both moist meadows along rivers and drier chalk downland can support an array of bee-fly species:
– The common bee-fly and stripe-headed bee-fly thrive in grasslands. Food plants include clovers, hawkweeds and knapweeds.
– The dotted bee-fly occurs in chalk downland sites where bulb species like fritillaries provide nectar sources.
Adult bee-flies seek warm sheltered spots among grass tussocks for overnight roosting.
Coastal habitats
– Coastal grasslands, dunes, cliffs and shingle support populations of the large bee-fly. It is a coastal specialist in Britain.
– The larvae develop in deep-rooted flowers like yellow-vetchling and sea pea which grow on cliffs and dunes. Adults visit early flowers including gorse and cow parsley.
– Sea cliffs provide crevices for overnight shelter and hibernation.
Gardens
Gardens can be attractive for common generalist bee-flies like B. major and B. minor which have adapted well to urbanization:
– Early emerging adults are attracted to flowering shrubs like Mahonia.
– Garden herbs such as thyme, rosemary and winter-flowering heathers provide nectar sources.
– Uncultivated areas provide larval development sites. Log piles, sheds etc. offer roosting sites.
Threats and Conservation
Some of the main threats facing bee-flies in the UK include:
– **Habitat loss** – Agriculture intensification has led to destruction of flower-rich grasslands, a key habitat for many species. Development pressure also threatens coastal and chalk downland sites.
– **Pesticide use** – There is evidence that pesticides reduce survival of beefly larvae developing in floral habitats. Adult flies may accumulate toxins while feeding.
– **Climate change** – Hotter drier summers could desiccate larval microhabitats in flowers and negatively impact development. Phenology mismatches may occur between flies and food plants.
– **Invasive plants** – Non-native species can crowd out native larval host plants e.g. Himalayan balsam replacing vetch species. This can put pressure on specialized bee-flies.
Various conservation actions can help support beefly populations:
– Protect key habitats like species-rich grasslands through designation as nature reserves. Implement sympathetic management.
– Create new areas of flower-rich habitat in the wider countryside through agri-environment schemes.
– Manage woodlands to maintain open glades and dead wood habitat. Leave old trees with holes standing.
– Avoid use of pesticides in areas where beeflies are known to breed.
– Monitor populations and distributions, especially of rare species like the dusky bee-fly.
– Raise public awareness of bee-flies through events, interpretation etc. Encourage bee-fly friendly gardening.
Bee-flies and Humans
Cultural importance
– Ancient Egyptians associated bee-flies with the gods Horus and Neith because of their supposed magical healing powers. Amulets representing bee-flies have been found in tombs.
– Beeflies are depicted in some Native American cultures, representing spirits of dead warriors. Their bold patterns were used in body art.
– In parts of Asia including China, drinking a powdered mixture of bee-flies was believed to confer resilience and energy. Dried fly parts were used in traditional medicine.
Scientific research
– The development of very long proboscises in certain beeflies has made them a model study system in evolution and co-evolution research.
– Scientists have investigated the neurobiology behind the hovering flight capabilities of flies like Bombylius major. This research has applications in robotics.
– Analysis of the chemical compounds in bee-flies showed that they produce antimicrobial substances. Further research could have pharmaceutical uses.
Potential risks
– No species of beefly poses any risks to human health or activities. They have no sting and are harmless if handled.
– A few species are parasites of bees but do not cause significant damage to hives or commercial species. Some may actually control populations of native solitary bees.
– One possible minor irritation is the tendency of beeflies to fly close to people’s faces, especially in spring. This is just investigative behavior rather than aggression.
Conclusion
The UK hosts a diverse array of bee-fly species with some interesting ecology and complex life cycles. These harmless insects make important pollinators of early spring flowers, as well as being fascinating subjects for scientific study. Protecting habitats like ancient woodlands and flower-rich grasslands is key to conserving our beefly fauna for the future. Their unique appearance and buzzing flight should be appreciated by anyone exploring the British countryside in spring. With increased awareness of these unusual flies, they can continue to fill their vital ecological roles.
