Lestidae of Finland: Lestes sponsa

Lestes sponsa, f, Helsinki 10.7.2012

Lestidae of Finland consists of four species that fall in two genera: 3 species in genus Lestes and one species in genus Sympecma. Out of these, the most common species by far is the Common Spreadwing/Emerald Damselfly, sirokeijukorento, allmän smaragdflickslända, Lestes sponsa (Hansemann 1823). The Lestidae are a sister group to all other damseflies (Zygoptera), and their internal taxonomy seems a bit freaky (Dijkstra & Kalkman 2012).

Ubiquitous and common, sponsa ranges from South Coast to Lapland and from Ilomantsi to the West Coast. It is also the most common Lestes in most of Europe, and one of the most common Odonata species in the northern Europe. It lives in all kinds of lentic waters and slow-flowing rivers, only missing from some oligotrophic and/or large lakes. It is an autumn species, with emergence beginning in late June; last fliers are usually seen in September.

Sponsas can be very numerous, and congregations of hundreds and thousands are not rare. They often oviposit in groups. Large numbers can be seen around small, fish-empty and sometimes ephemeral pools and ponds, especially those with rich vegetation, such as Typha stands.

Identification of Lestes sensu lato in field is quite straightforward. Metallic, green gloss, spread wings and goofy jizz usually make identfication straightforward. Species identification can be bit more challenging. Hand charasteristics include five-cornered wing cells somewhere and other relatively useless features. Just look at it! European Odonata are easy.

Sponsa is usually identified by the combination of following features:
1) Very common. Although not a basis for identification, about 95 - 99 % of Lestes individuals in Finland are sponsa. Maybe even more. So you start with the assumption that it is probably sponsa.
2) Females: pale antehumeral stripes (cf. Lestes dryas). Dark back of the head (cf. Lestes virens). Dark pterostigma (cf. virens). There is a lone dark spot at the base of the first pair of legs. The ovipositor's size is useful, if one has experience, but I would caution against using it as a primary means of identification if you are a novice with sponsa/dryas -pair!
3) Males: young look like female sponsa. Adults have no metallic sheen on the S2, instead the entire segment is pruinose (cf. dryas). Back of the head is dark and pterostigma dark (cf. virens). Males' lower appendages are relatively straight, not strongly curved towards each other. Be careful with young sponsa males, where their pruinosity is not yet fully developed and they can thus resemble dryas!

Dryas is scarce, virens is a vagrant, and our fourth Lestid, Sympecma paedisca, resembles Enallagma more than a lestid. More of them later.

References:
Dijkstra, K.-D. B., Kalkman, V. J. 2012: Phylogeny, classification and taxonomy of European
dragonflies and damselflies (Odonata): a review. - Organisms Diversity and Evolution (in press) Link