Types of leafmines

Leafmines are the characteristic galleries created on either the upper or lower surfaces of leaves. Most mines are created by the internal feeding of lepidoptera larvae within the leaf, but others are the result of coleoptera, diptera or hymenoptera larval stages. Only lepidoptera are dealt with here.

In the majority of cases, leafmines are created by the larva eating within the leaf, between the upper and lower surfaces, but some species' mine other parts of the plant and even the seeds. The resulting mine is frequently obvious to the eye, even though all leafmines are generally small.

Leafmines can be categorised into two general types, known as gallery mines and blotch mines.

Most gallery forming leafminers are either Stigmella, Ectoedemia or Bucculatrix species, most of which are indeterminable to identify to species level without dissection of the adults genitalia. But even those species constructing similar gallery mines within leaves of the same foodplant, can often be separated by the method of frass dispersal within the mine. Even if frass dispersal is linear, the width of the frass in relation to the width of the gallery can sometimes clinch the identification. If present, larval colouration or head colour, is another good key to identification and neccessary in some of the Hawthorn feeding Stigmellas.

Blotch mines again show considerable variation in size and shape and can be on either the upper or lower surface of the leaf. Frass within blotch mines is often dispersed unevenly, but some of of the Eriocranias produce distinctive "arcs" of frass, which helps towards the identification. Frass patterns or distribution in old mines, often cannot be used as an aid to correct identification, as the frass dries up and falls to the lower part of the leafmine.

Blotch mines produced by larvae of the Coleophoridae are more unusual in that the larva feeds inside the leaf, but constructs a protective case from a section of leaf in which it lives and feeds from. Experience gained through working with leafminers, will eventually mean that Coleophora blotch mines are distinctive enough to distinguish from other blotch mines at once.

Searching for leafmines

Searching for leafmines will always be productive. Familiarity with larval foodplant is essential and a bit of background research prior to going out certainly helps and often pays dividends. Visit the British Leafminers website for further details.

The first leafmines can be found in the depths of Winter, when the white upper surface gallery mines of Stigmella aurella, are easy to find on Bramble. Searching for Stigmella aurella, will usually reveal the elongated blotch mines of Emmetia marginea, another common Bramble feeding species. By late April, several of the Eriocrania leafmines will begin appear on Birch and Stigmella lapponica is another early species to look out for. As the Summer progresses, the potential number of species to be found increases dramatically and by the Autumn, as moth numbers at light traps begin to decline, there is still much of interest that can be looked for.

While ever there are leaves on trees, it will always be possible to look for leafmines. But even when the last of the leaves have fallen, there is still a number of mines that can be looked for. Looking on the fallen leaves of Oak for characteristic 'green islands' will often reveal the presence of species such as Ectoedemia subbimaculella and Ectoedemia heringi, two common leafminers. The 'green island' caused by the larva of Ectoedemia argyropeza, is shown in the accompanying photograph. These are surprisingly easy to find when the moth is present at a site on fallen Aspen leaves.

The list is alphabetical by species and uses the new numbering system (left column) and scientific species names, as used in the Checklist of the Lepidoptera of the British Isles (D. Agassiz, S. Beavan, R. Heckford. 2013). The old Bradley and Fletcher numbers are shown in grey. Months when the leafmines of any species should be looked for, are highlighted in grey.