Archive
BIGGEST AND SMALLEST BRITISH INSECTS
18/09/2025
Staying with an entomological theme, I have been wondering which of our native insects (in the strict scientific sense) is the largest and which the smallest. A little research provides an interesting answer.
Ordering our insects by the heaviest (i.e. by their mass), the biggest is one of the Coleoptera, the male stag beetle Lucanus cervus which can be some 8cm long and weigh 12 grams or even more. The bush crickets (Orthoptera) also have some large species, for example the great green bush cricket Tettigonia viridissima (Linnaeus, 1758) whose females can grow to over 40mm long, and the cockchafer or May bug Melolontha melolontha Linnaeus, 1758 which is a familiar chunky beetle to about 30mm long.
Our smallest insects are within the hymenopteran order of fairyflies, the Mymaridae, really tiny parasitic wasps of which several species are less than 0.5mm in length. These are not very well known or studied but, as an example, a candidate for the least massive would be Alaptus fusculus Walker, 1846. It is an ova parasitoid[1] of certain species of bark lice (Mesopsocus spp.) and minute at c. 0.2mm long (i.e. 2μg) and of vanishingly small mass. I do not have a photo but Wikipedia has an image of a fairyfly which I have posted here to give you an idea. The size difference is more than a million times in mass.
[1] An organism which, after feeding on it, kills its host. Below is a graph on log scale to illustrate the difference:
To get a better idea, here is a simple silhouette illustration of a stag beetle and a fairyfly on a relative scale graphic. At scale, the fairy fly is just a dot.
Betts Ecology appreciate the amazing diversity of nature and do our best to protect the tiny as well as the huge. We are always interested in unusual insects you might see – send us a photo with information on when and where you saw it.
