Tuesday 29 November 2016

Silky Lacewings (Psychopsidae)

I spend a lot of time trying to explain to people just how mind-numbingly diverse invertebrates can be.

And they are; take the lacewings - quite small, as insect orders* go, but still have over 600 species recorded from Zambia or a neighbouring country (based on information from the Lacewing Digital Library, an excellent resource that I probably rely on far too heavily).

So it's always pleasing to realise that I have encountered every member of a specific clade that enters the country, whether it's all the subspecies of a species, all the species of a genus or - in this case - all the members of the family.

Even if that family is the Psychopsidae, one of the least represented Neuropteran families in the continent with only eight species entering Africa, and only two likely to occur in Zambia (i.e. recorded in Zambia, or in multiple disjunct, bordering countries, in areas of comparable climate.

Before I bore you too much with endless text, here's one of them:

Silveira marshalli (McLachlan, 1902); came to lights on an unnamed tributary of the Luangwa. 

These eight species in three genera are actually a rather hefty share of the global diversity; both Australia and Asia have only a single genus each (although Australia's Psychopsis contains half of the global species).

They are extremely distinctive lacewings, at least within the region, instantly separated from all other lacewings by their broad, hairy wings; while some 'green' lacewings (Chrysopidae) and the Osmylids (no common name) are rather broad shouldered, none are quite so dramatic as these; they also tend to have rather longer antennae, and their bodies extend more noticeably in front of the wings.

Most are associated with woodland, where they have been suspected to pre-powder their eggs with vegetable matter, and fire them into leaf-litter while in flight (for more on that - and a general overview of the family - see Oswald, 1993); these presumably hatch into the usual, hyper-predatory little monsters that lacewing larvae usually are.

Formally, only one species is recorded from Zambia; but given that Zambia's predominant natural habitat is Miombo woodland (accounts vary as to whether this is a fire-dominated moist savannah, or is a type of subtropical deciduous forest currently massively degraded by man-made fires), it wasn't a stretch to assume that Silveira marshalli (McLachlan, 1902) - recorded from Botswana, Zimbabwe, South Africa and Zaire - would be present; it is, and comes to lights in numbers in forested parts of Eastern and Muchinga provinces.

As for the other, Zygophlebius leoninas, Navás, 1910 - easily the most widespread African species, probably the most widespread species in the entire family (although as you can read in Oswald, 1994, there is a bit of a mess where it comes to records of this and the genitally-distinguished Z. zebra (Brauer, 1899) - I'd really like to be able to credit its appearance at a kitchen window in the increasingly developed Chongwe district to my ongoing tree-planting (and native-tree-encouraging) efforts, rather than the more likely conclusion that it's just another species that is slowly disappearing as every acre of ground is agriculturally exhausted and covered in concrete.

On that somewhat bleak note, here it is:


Zygophlebius leoninus Navás, 1910 in Chongwe District, Lusaka, Zambia. 





















*Main taxonomic rankings, in order from largest to smallest: Domain (e.g. Eukaryota); Kingdom (e.g. Animalia); Phylum, (e.g. Arthropoda); Class (e.g. Insecta); Order (e.g. Neuroptera - lacewings); Family (e.g. Psychopsidae - Silky Lacewings); Genus (e.g. Silveira or Zygophlebius) and Species (e.g. Silveira marshalli)

Wednesday 23 November 2016

The Stilt-Legged Flies - Micropezidae

Flies.

True flies, to be specific; the two-winged members of the order Diptera  - I feel like we've neglected them a little*. They are, after all, the second largest order of insects in terms of described species, and - as I'm currently trying to come up with a rough key to the families of flies in Zambia, I'm currently painfully aware of just how diverse they are.

Based on recorded distributions of the 159 or so fly families globally (some are sometimes subsumed, there should be some 100 - not roughly, that is actually the number - families of flies present in Zambia.

Note that that isn't 100 'types' of flies, or 100 'species' of flies, but 100 families of true flies; some of which contain hundreds of known species in the region, some of which are only separable by dissection of the genitalia (ow) - and this may only represent a fraction of the actual diversity of this (understudied) country.

As you might imagine, these can be a nightmare to identify - even in groups where species are physically very different, because many taxonomists of history were so concerned with minute differences of genitalia that they neglected to mention the massive external differences between related genera and species (this is essentially why we have voucher specimens and museums: so that authors who think one feature is the most important don't end up making a taxonomic group completely unworkable. It doesn't always work).

Many of these 100 families, however, have only a few species in the region: while there are several dozen species further North in the continent, Southern Africa hosts only six species of the family Micropezidae, and records indicate that Zambia hosts even fewer.

To interrupt this long block of text, here's one of them: 

Mimegralla, probably Mimegralla fuelleborni (Enderlein, 1922, photographed on a farm outside of Mazabuka. 





You'd think with so few species, we'd know just what they do with their daily lives.

We do know a little, but the trouble with these flies is that they are fairly small and inconspicuous, and rarely - if ever - common, so that even with only six (known) species in the entirely of Africa below the Zambezi, the most insightful observation that the-usually-helpful Barraclough** made into their life histories was that their curious white fore-limbs could to be some sort of imitation of ichneumon wasps. Quite how it would benefit the fly to imitate a wasp which cannot sting remains unclear.

As to the rest? Well, one Indian species (Mimegralla coerulifrons (Macquart, 1843)) is a pest in commercial ginger and turmeric farming, and as a result has been quite well studied, and adults have been variously stated to be predatory (which, although this particular species location and behaviour suggested that it was there for the aphids, is doubtful applied across the entire family), and the suggestion that larvae are saprophagous (same link as the last, even though I should chase it the source, I know).

And if we throw in anecdotal claims, it gets even more confusing.

So let's not. Let's just enjoy them.

Here's another, this time Erythromyiella rufa (Hennig, 1935) from Lusaka South:





And, well, at some point I must learn how to write some sort of conclusion to these things instead of just trailing off..










*Not entirely - we have covered a few before - a long, long, long time ago: a rather unusual 'flesh fly' -  Dolichotachina caudata - which probably, like its closest well-studied relatives, acts as a cuckoo to burrow-nesting wasps; the extraorinary long-horned cranefly 
Megistocera filipes, never previously recorded in Zambia; the bizarre Stalk-eyed Diasemopsis meigenii, four hoverflies all trying - with varying success, to convince us that they are wasps or bees (Senaspis haemorrhoaHelophilus pendulusEpisyrphus balteatus and Metadon inermis), and the inexplicably named 'centurion' Chloromyia formosa


**If you are interested in Micropezidae south of the Zambezi and Kunene rivers (i.e. Zimbabwe, Botswana, South Africa, Southern Mozambique and probably-not-Namibia-because-they-are-mostly-forest-associated, do download the Barraclough (1996) paper, as it contains descriptions of all 6 regional species, and a decent key. I suspect that in the Northern parts of Zambia, Mozambique and Malawi, we get a few more recently-described (or undescribed) species - Tanzania certainly does - but for Southern Africa, this seems to be your lot. 

Monday 14 November 2016

The Net Casting Spiders (Deinopidae)

Meet Deinopis Macleay, 1839. 

Male. Photographed in Chongwe District, Lusaka Prov., Zambia, November 2016, using Olympus E-420 and 3 KOOD lenses. 

Deinopis is the more iconic of the two genera of Net-Casting Spiders, distributed throughout the warmer regions of the world; it lends its name to their family (Deinopidae), and is the source of another common name for the family - Ogre-faced Spiders - and, locally at least, species of this genus are physically much larger, and difficult to overlook. This impressive male, found wandering on a driveway on a hot, humid night, had legs that spanned over 5cm.





To put this in context, his legs are very long; unusually long, you might think (if you are used to thinking about these things) for a spider that neither lives in caves (where anything and everything has a license to have very long legs) or live in a web





But this little Kangaude (Chewa - spider) does build a web. To those who know a little about spiders, this doesn't really resolve much: while his legs make slightly more sense, now, his eyes become something of a puzzle: of the other spiders blessed with such large and conspicuous peepers, most belong to either the Jumping Spiders (family Salticidae) or the Wolf Spiders (family Lycosidae); the vast majority of which are active, free-living predators, which use their eyes to see, hunt and capture prey - or, in the case of most jumping spiders - to communicate via semaphore.

To explain all of this, we have to turn to Deinopis' smaller and more abundant relative - and the only other genus in the family - Menneus Simon, 1876 - for a practical demonstration: 


Photographed in Chongwe, Lusaka, Zambia in April 2015. 

As already mentioned, one of the common names for this family of spider is Net-Casting Spider (and I will eventually find the direct Chewa translation for that, in theory); and they do precisely that; they wander around in search of a crossing point of nocturnal insects to wander through, and then, suspended above it by a simple thread, they spin an entire web between their (very long) front legs, and they wait.

And they wait.

Eventually something wanders past, and, seeing the movement, they whip down the net and voila, pre-wrapped meal - and a unique method of hunting that needs both a web and excellent vision.
Menneus - note the smaller eyes and the abdominal 'hump'. 




It is worth noting that Menneus' vision isn't quite like Deinopis'; they are probably most easily identified, in fact, by lacking the massive enlargement of the posterior median eyes seen in Deinopis; their eyes are still larger, on the whole, than those of most web-spinning spiders, but if it wasn't for their extraordinary webs, and the curious protuberances from their abdomen (earning them the alternative names of Camel-backed Spiders and Hump-Backed Spiders), they might be mistaken for free-living nursery-web spiders (family Pisauridae). 













Although identification to genus for this family is extremely easy - especially now that Avella and Avellopsis have been shoehorned into Menneus - you'll notice that I haven't listed a species name for either of our two guest-stars; although none appear to be recorded specifically from Zambia, a number of species are recorded from neighbouring countries and the wider region (see the World Spider Catalog page on the family); and - as the spiders are inconspicuous, nocturnal and easily overlooked - there is every chance that these do not belong to described species at all.

So I'll get back to you on that.