The singing lacewings

Adult common green lacewings, Chrysoperla carnea, are starting to search of suitable hibernation places, and they often come inside buildings. This one was inside my office the other day and allowed me to take her portrait. C. carnea was once thought to be a single widespread species but it is now known to be a species complex, an aggregate of morphologically very similar species that often co-exist.  Courtship involves males and females drumming a song on the substrate where they are sitting with their abdomens. The vibrations are detected by organs in their legs. Males and females respond to each other's drumming in a complex duet and only when they sing the same song does the courtship ends in mating. The different species in the complex have different songs, with characteristic drumming frequencies. The figure below illustrates the differences between the six biological species within the C. carnea group that are recognised in Europe.

 

The drumming songs of European cryptic species of Chrysoperla carnea sensu lato (from Henry et al in

Lacewings in the crop environment By Peter K. McEwen, T. R. New & A.E. Whittington)

Both C. lucasina (probably the top photo) and C. c. 4 "motorboat" also known as C. c. "sensu stricto" have been found in the U.K. C. lucasina does not change colour in winter, has "pointy wings" and a dark membrane between the sternites and tergites in the abdomen. C. carnea "sensu stricto" has rounded wings, changes colour and does not have the dark membrane. However, individuals that do not fit either of the species are often found in the U.K.

As their distinctive songs are difficult to tell apart for the untrained eye (ear?), and the morphological characters that do differ between the cryptic species are sometimes not apparent or distinctive enough, identification to these lacewings on the field is tricky. 

 C. carnea 4 "motorboat" may change colour prior hibernation (photo from 10 October 2011).

Lacewing larvae, distinctive large jaws and covered on detritus, which often are the shrivelled skins of the aphids she feeds on.

Earwigs and the conundrum of cryptic species complexes

While collecting grapes, I came across a group of adult earwigs. Earwigs are insects of the order Dermaptera, characterised by the presence of  a pair of sexually dimorphic appendages at the end of the abdomen called forceps. Female forceps are more or less straight (above), while the male's (below, with two males of different sized forceps) are larger, curved and furnished with a pair of teeth. F. auricularia males are also dimorphic, with a large forceps form (macrolabic) and a small forceps form (brachylabic).

Earwig forceps are used for defence - they readily raise their forceps when disturbed - and are involved in reproduction, males fight using their forceps as weapond and display them to females during courtship. Males with larger forceps seem to be preferred by females, so they appear to have evolved through sexual selection. Earwigs are also unusual amongst insects in their level of maternal care. Females build a nest chamber, and stay with their eggs after oviposition, they continuously groom their eggs keeping them fee from fungi and sit atop them, occasionally moving them within the nest to areas of optimal temperature and humidity conditions. They also provide their larvae with food and defence for several instars. In 1998 Thiery Wirth and colleagues, while examining the inheritance of brood number variation in the common European earwig Forficula auricularia through laboratory crosses, found that single brooded and two-brooded forms did only rarely produce offspring. Further genetic analyses confirmed that F. auricularia is made of two cryptic species. Cryptic or sibling species are species that cannot be distinguished easily by their morphology, although they are reproductively isolated and might differ in song or pheromones so, despite their similarity to our eyes, males and females do not recognise each other as mates. Cryptic species are very common among many invertebrate groups and are a nightmare for the biologist trying to understand the behaviour or ecology of a species, as it is often impossible to be sure that one is dealing with a single species without using genetic tools. In F. auricularia, the two cryptic species have not been formally described, but one, referred to as species A, prefers colder climates or higher altitudes, females are single brooded, and tend their clutch for longer and the larvae disperse later; while species B typically lives in more temperate areas, females produces two broods, tends its brood fo r a short time and has an earlier larvae dispersal. In his PhD thesis, Gordon Brown concludes that a single species inhabits the UK, and this is the single brooded species A. At this time of the year, males and females are found above ground and they will be mating. Although males stay with the female and may help with nest building, they are unlikely to make it through the winter and are excluded from the nest once oviposition takes place, while females will overwinter in the nest, where they will lay their eggs early in the year and tend the next generation of earwigs.

References
Guillet, S., Guiller, A., Deunff, J. & Vancassel, M. (2000). Analysis of a contact zone in the Forficula auricularia L. (Dermaptera: Forficulidae) species complex in the Pyrenean Mountains. Heredity, 85 (5), 444-449 DOI: 10.1046/j.1365-2540.2000.00775.x
Thierry Wirth, René Le Guellec, Michel Vancassel & Michel Veuille (1998). Molecular and reproductive characterisation of sibling species in the European earwig (Forficula auricularia) Evolution, 52 (1), 260-265.
Gordon Brown (2007) Sperm competition and male forceps dimorphism in the European earwig Forficula auricularia (Dermaptera: Forficulina). PhD Thesis University of St. Andrews.