Wednesday, 21 September 2011

Office jumping spider

I watched this tiny jumping spider this morning crawling up my office wall. It must have been 4 mm in size. It carried its dark front pair of legs pointing forward, which gave it a crab like appearance, but its lovely face with large, front facing middle pair of eyes were unmistakable as a jumping spider. It was a male Pseudeuophrys lanigera, a synanthropic species, that is, often found in or around houses.
 The species originates from Southern Europe, and has spread throughout Europe during the last century. In the UK is also expanding north.
 Males have a striking combination of a red face mask, a white moustache, white palps, and robust, black front legs, females are a bit more subdued, and their front pair of legs is annulated as the others.
the male on top view
female (9/04/11)
same female on windowsill (9/04/11)

Tuesday, 20 September 2011

A tree bumblebee queen

 This tree bumblebee, Bombus hypnorum, queen has been visiting the garden in the last couple of days, with her fresh, striking tawny/black/white pattern very apparent. The last time I saw this species this year was in July, when males patrolled in the garden and queen bees could be seen searching for nest (or hibernation sites). August, three years in a row, yielded no sightings. Yesterday's queen visited Erysimum "Bowles's Mauve". This perennial wallflower, which often appears in BugBlog shots, and I highly recommend in any wildlife garden, has a very long flowering season and attracts a range of solitary bees and bumblebees, hoverflies and butterflies.
This graph shows the number of days per month I've seen this bumblebee in the last three years. Workers are active during May and June, most of the July activity is males marking and patrolling their flight paths and queens. The rest of the sightings in the autumn and early spring are queens feeding or nest searching.

Sunday, 18 September 2011

The hoverfly nightmare

Yesterday morning I found this Ectemnius wasp on a plant pot. Usually, they are very active and are flighty, but this one was still cold and let me take some close ups. Ectemnius are digger wasps that hunt flies - including hoverflies - for their larvae to feed. They dig a tunnel in wood and stock cells with flies, laying their eggs in them. They are several similar species, that can only be distinguished under the microscope. The microscope, however, is not needed to appreciate two of the weapons that these wasps use for hunting: their amazing, large, envolving eyes - note the antennae nicely folded between them, not occluding their field of vision, and their fearsome jaws, folded under their head.

Saturday, 10 September 2011

A bit of slug romance

ResearchBlogging.orgAs their snail relatives, slugs are hermaphrodites, each individual producing eggs and sperm. Although some species regularly self-fertilise, in many others, individuals  - given the chance - will trade sperm with other individuals they encounter. I came across this pair of courting slugs under a fallen apple an evening last week. They are Deroceras panormitanum (thanks to Fauna, from WAB for the ID). At the right time of the year, and when meeting a potential partner, these slugs crawl in circles, producing and eating chemicals mixed in their respective mucus trails, before mating happens. The outcomes of courtship and mating are diverse: the slugs are able to mate repeatedly and use sperm from several donors to fertilise their eggs, or they might decide not to give sperm to its partner, or digest the sperm obtained and self-fertilise. This means that, despite being hermaphrodite, a slug can decide if to act only as male (digesting the partners sperm but providing its own), as female (refusing to give sperm, maybe preferring to save it for a better partner) or as both. This can create conflict between the partners - each with their own interests - and has been hypothesized to spur an "arms race" - or "genitals race" if you wish, and has led to the evolution of a range of bizarre copulatory structures and complex mating courtships.
 Heike Reise has reviewed and described the behaviour of these diverse genus of slugs and summarized courtship and mating as follows:
(i) Precourtship phase: the partners encounter and investigate each other.
(ii) Courtship phase: both partners have their sarcobelum protruded from the genital opening and assume a position with their genital pores facing each other, forming a circle or yin-yang configuration. 
(iii) Copulation phase: the slugs evert their penes, entwine them, and mutually transfer the ejaculates from penis to penis (there is no intromission). 
(iv) Withdrawal phase: the penes are retracted together with the attached sperm masses.

After coming across a potential partner or trail, some behaviour follows. This species has a flattened tail, which is enlarged during courtship and waved from side to side. These movements increase the chances of contact with the partner's tentacles. If the leading individual is ready to mate, it eventually turns round and starts following the second individual, forming a circle. Both individuals then evert their sarcobellums - as seen in the top shot - a solid, mobile structure in the genitalia which produces chemicals, that are exchanged during their circling behaviour. The sarcobelum is very active during the courtship, tracking closely the partner tail end and stroking it, at the same time that smears the partner with chemical secretions. In this species, courtship can last over an hour, followed by a relatively quick copulation (a few minutes), in which the slugs genital openings become very close, actual penises - bluish, transparent masses - are everted and entwined with the partners and sperm are exchanged externally. These slugs also have a penial, multifingered gland, that they also evert after insemination and lay over their partner's back, transferring some secretions. The function of this gland has been suggested to be equivalent to the snails' dart, the smeared chemicals on the partner might increase the chances of paternity. The slugs above were in the courtship stage, but unfortunately, by the time I went out again to check on them, they had disappeared.

Heike Reise (2007). A review of mating behavior in slugs of the genus Deroceras (Pulmonata: Agriolimacidae) American Malacological Bulletin, 23, 137-156
Benke M, Reise H, Montagne-Wajer K, & Koene JM (2010). Cutaneous application of an accessory-gland secretion after sperm exchange in a terrestrial slug (Mollusca: Pulmonata). Zoology (Jena, Germany), 113 (2), 118-24 PMID: 20202803