Northamptonshire's Craneflies

Northamptonshire's Craneflies

John Showers, Northants County Diptera recorder, gives an insight into Craneflies, and the recording scheme, and hopes to encourage more people to learn about these fascinating insects.

With this year’s publication of “British Craneflies” by Alan Stubbs1, it is an opportune time to review the cranefly fauna of Northants, such as we know it, and to encourage more naturalists to start recording these insects. The Cranefly Recording Scheme covers six families of flies. Four families make up the true craneflies in the superfamily Tipuloidea. These are the Tipulidae (Long-palped Craneflies), Cylindrotomidae (Damsel Craneflies), Pediciidae (Hairy-eyed Craneflies) and Limoniidae (Short-palped Craneflies). In addition to these four families two other families are considered “honorary” craneflies: Trichoceridae (Winter Gnats) and Ptychopteridae (Fold-winged Craneflies). In total these families comprise about 350 species in the UK, of which about a third have been recorded in Northants.

Many craneflies have fairly specific habitat requirements in the larval stage and so can be good indicators for assessment of areas for conservation purposes. Some breed in dead wood and are associated with continuity of mature woodland. Many old deer parks as well as woods contain ancient trees and may have interesting craneflies present. Another suite of species are associated with damp soils, some with basic conditions and others with acidic conditions. In general craneflies do best in warm, damp conditions but there are species associated with uplands or which fly in the cooler months of the year. Indeed most Winter Gnats, as their name suggests, fly in sunny weather in the Winter months. A few craneflies have aquatic larvae but most prefer damp soils or leaf litter, damp mosses or damp wood in which to breed. Wet flushes and trickles down rock faces can produce some unusual species. There are species, however, which occur in drier areas, usually in Spring before the summer sun fully dries out the ground.

The adult cranefly season really gets going when hawthorn starts to flower but there will be some species out before that. The season usually ends in late Autumn depending on local weather conditions. Indeed craneflies can make up a significant part of the Autumn diptera fauna. Many species have specific flight periods but some may have more than one peak in the year. Craneflies usually avoid hot sun so in these conditions it is best to seek out shady areas, especially if the ground remains damp. Mossy woodlands and shaded stream banks can be very productive areas. Many craneflies fly at dusk and at night and can be attracted to moth traps so moth trappers can make a big contribution to our knowledge of the distribution of species. Indeed, the Pitsford Water moth traps have yielded a few county firsts since we started recording the by-catch.

The county species database contains records of craneflies going back just over 20 years but regular recording has only taken place for about 10 years. The attached map shows the distribution of species diversity in the county. There is clearly a need for a lot more recording before we have a good picture of our cranefly fauna. Much of the county has no records and most of the rest has relatively few records, mainly of common species. The data shows that the ancient woodlands, including parkland, and our wetlands are most productive. However this could be down to recorder bias as these are the areas that are most visited.  There is great scope for recorders to start to fill in the blanks. As with many other taxa the south-west of the county is under-recorded.


The distribution of cranefly species diversity in Northants. White squares represent 1-13 species, dark red 52-65 species

Identification of craneflies is reasonably straightforward for most species once you have got to grips  with understanding the wing venations and markings. Most can be identified in the hand with a lens with some experience, although it is best to try to catch some and examine them more closely when you first start out. A few of the smaller species do need higher power magnification to see critical features, especially the male genitalia, but these can be tackled as more experience is gained. The best guide to identification is Alan Stubbs’s “British Craneflies” and this can be bought at a significant discount by members of the BENHS or Dipterists Forum. The keys in this book have been developed over several years with a lot of usage-testing so are fairly straightforward to follow. An earlier version of the keys can be downloaded for free from the Cranefly Catalogue of the World2 by searching for Stubbs and Kramer in the publications section of the site.

Pete Boardman’s “Shropshire Craneflies”3  also has keys for the species most likely to be found in our area, although personally I find the keys harder to use. The book does have some excellent photos and descriptions to help confirm identification. The best way to get started with craneflies is to attend an identification workshop where you get the chance to see the features described in the keys and any misunderstandings can be sorted out. The Wildlife Trust will be hosting workshops in 2022 and other workshops may be run by the Dipterists Forum, Field Studies Council, BENHS and the Natural History Museum.

Our most familiar cranefly is the large “daddy long-legs” that emerges in the Autumn from grasslands, including lawns. Its larva is the leather jacket that feeds on roots of grasses and cereals and can be an agricultural pest. This species is Tipula paludosa (Meadow White-stripe). However, it is easily confused with the equally common T. oleracea (Marsh White-stripe), which flies from late March to Autumn. In mid-October and November a third species, Tipula subcunctans (Dark White-stripe) is on the wing so care is needed to separate them. No such problem exists  with the common Limonia nubeculosa (Three-banded Limonia). This beautiful medium-sized cranefly of woodlands has delicately mottled wings and three distinctive dark bands on each of its femora, a combination unique in British craneflies. Many of our woodland craneflies have mottled wings, probably to help camouflage them in dappled light. Some species have bold patterns, like the large T. maxima (Giant Long-palp) which is found in many of our wetlands. Such species can be identified by the wing pattern alone. 

So far we have found two species of comb-horned craneflies in Northants. These colourful insects can easily be mistaken for large wood wasps or ichneumons and the females have impressive ovipositors which could be mistaken for stings. They are quite harmless however. Both species are Nationally Notable and have been occasionally recorded in a number of ancient woodlands and parks in the county. They breed in rotting wood. Ctenophora pectinicornis (Orange-sided Comb-horn), usually breeds in rotting branches in the tree canopy, whereas Dictenidia bimaculata (Twin-mark Comb-horn) tends to go for smaller tree trunks that are well rotted.

Birch is a particularly favoured species. They get the common name of comb-horn from the antennae of the males. Each antennal segment has appendages hanging down, giving a comb-like profile. If you have access to ancient woodland or parks it is well worth looking out for these spectacular insects between May and July. Try to photograph them to get a reliable identification. Many craneflies can be reliably identified from good photos, especially if the wings are spread so the veins and any pattern can be clearly seen.

Another colourful set of craneflies is the black and yellow tiger cranefly group belonging to the genus Nephrotoma. The most familiar is the early spring N. appendiculata (Inverted-U Tiger). This boldly marked cranefly is basically yellow with strong black markings. As its common name suggests, it has an inverted U mark (or an n) on the side of its thorax. Several other species emerge in early summer, including N. flavescens (Primrose Tiger), a particularly bright cranefly with a black ace of spades mark on its head. It commonly occurs in gardens.

Some craneflies may be easier to find as larvae, rather than adults. For example, Graham Warnes has recorded the spectacular larva of Phalacrocera replicata (Smooth Damsel) in a number of ponds in Yardley Chase but we have never found an adult.

I hope this short introduction to craneflies will encourage more recorders to take an interest in the group. Alan Stubbs has given English names to all our species, although few dipterists will recognise them at present. However it may encourage people who are put off by scientific names. There is much to learn about their life-cycles as well as their distribution so they can make a fascinating subject for naturalists.
1.    Stubbs, A.E., 2021. British Craneflies. BENHS. Reading
2.    Cranefly Catalogue of the World.
3.    Boardman, P., 2016. Shropshire Craneflies. Field Studies Council. Telford