Zooming in on the Hangers On

My garden compost bin has been producing clouds of Drosophila. Before it cooled off I had to stand back when I opened the lid to avoid being covered in flies. Over the weekend I took a closer look. They turned out to be a mixture of two species, Drosophila immigrans and Drosophila hydei, both cosmopolitan tramp species. 

Looking closer, most of the D. hydei were carrying a good load of mites. The good folks of the Facebook Soil Biodiversity UK group were able to identify these for me as Macrocheles spp. These are predatory mites which feed on nematodes, small worms, fly eggs and larvae and other tiny arthropods. They are strongly associated with ephemeral, nutrient-rich substrates such as leaf litter, decaying plant matter, animal dung, carrion, and animal or insect nests. A common behaviour in this group is phoresy - the mites attach to mobile carriers such as flies to travel from one temporary food source to another. Adult females are the usual dispersal stage, and phoresy is typically non-feeding transport rather than parasitism. Their reliance on transient resources makes rapid colonization and dispersal central to their life history: when a resource is exhausted, phoresy lets populations reach the next suitable habitat. 

Looking closer still and the mites were carrying a load of sac-like objects. They seem to be nematode dauer larvae, hitching rides from one compost heap to another. A dauer larva (from the German dauer, meaning "endurance" or "persistence") is a stress-resistant non-feeding third-larval stage that some nematodes enter when environmental conditions are unfavorable. Instead of progressing to adulthood, the worm halts development at this specialized stage. Dauer larvae do not feed and slow down their metabolism dramatically. They can survive for several months (up to four times longer than a normal lifespan), enduring harsh chemicals, desiccation, and extreme temperatures. Dauers actively seek out new environments; once they encounter favorable conditions (such as fresh food or a host), they exit the stasis, moult and resume normal reproductive development. The anti-slug nematodes you can buy are actually dauer larvae and another example was a dauer larva frozen in Siberian permafrost 46,000 years ago, when Neanderthals still walked the Earth, which was revived successfully (A novel nematode species from the Siberian permafrost shares adaptive mechanisms for cryptobiotic survival with C. elegans dauer larva. (2023) PLoS Genet 19(7): e1010798 https://doi.org/10.1371/journal.pgen.1010798).

Bear in mind that the mites eat ... nematodes amongst other things, so you could regard this as livestock farming - the mites pack dauer larva before going off on their Drosophila package tour, thus they have a food source when they arrive. And all  this is without looking for parasitic wasps utilizing the flies, mites and possibly even nematodes in my compost heap. Who knew my discarded banana skins were so interesting?

 

 

Pergamasus

 Every once in a while I have a crazy urge to deep dive into a new neglected taxon. Sometimes I resist. 

Back in lockdown I listened to an excellent online talk on mites, and since I regularly get them in vacuum samples, I was tempted, but managed to resist. Over the stormy weekend I was clearing a backlog of samples from the past year and in one came across this chunky red-ish mite. Given the weather, I took photos and posted them on the excellent Facebook Soil Biodiversity UK group asking for help. One of the experts there was able to identify it as a male Pergamasus spp. (Family Parasitidae). I'm very grateful, but I'm still not planning on working on mites (or Thrips, which are easier) very often. 

Pergamasus (suborder Mesostigmata, family Parasitidae) is a species-rich genus of soil-dwelling predatory mites. They are key apex micro-predators within the soil food web, primarily distributed across the Holarctic region. Relatively large for soil mites, usually ranging from 0.8-1.5 mm in length. They are typically well-sclerotized with a characteristic yellowish-brown to dark reddish-brown chitinous body. Broadly oval, somewhat dorsoventrally flattened, with robust legs adapted for rapid movement and grasping prey. Adults possess a large, rigid dorsal shield (single, continuous plate covering the back) or a deeply divided schizodorsal shield depending on the species. Females possess a distinct, triangular or acuminate genital shield (epigynium) flanked by metasternal shields. Male leg II is heavily modified into a grasping organ with pronounced skeletal spurs and apophyses used during mating. The chelicerae feature a modified spermatotreme for sperm transfer. Found in soil & litter layers, both nymphs and adults are fast-moving, voracious generalist predators feeding on a wide variety of soil micro-invertebrates. They use their powerful, chelate chelicerae to puncture prey and suck out bodily fluids.

Bhattacharyya, S.K. (1963) A revision of the British mites of the genus Pergamasus Berlese s. lat. (Acari: Mesostigmata). Trustees of the British Museum (Natural History).

 

The Softly Singing Spider

 Cann, A. (2026) The Softly Singing Spider. British Arachnological Society Newsletter, 166, 9.

click for larger image

Carnage in a flower pot

I spotted some strange Hymenopteran goings on on the side of a flower pot on my patio. On investigating, I found this female Common Black Spider Wasp, Anoplius nigerrimus, trying to fly with a large female Common Fox Spider, Alopecosa pulverulenta, considerably heavier than herself up under the rim of the pot. 

The excellent BWARS account for this species makes clear that they aren't too fussy about nesting spots. I interrupted her for a quick portrait, then put her back by the pot with the babyfood (which was done for, having already been paralysed). 

New Arachnid Recording Schemes Atlas

The British Arachnological Society recording schemes atlas has had a long awaited revamp and is now available, with 1.6 million UK Spider, Harvestmen and Pseudoscorpion records to play with. The new atlas is fantastic, with many ways to slice and dice the data. It's taken a huge amount of work to get to this and the team behind it are to be congratulated. It would be fantastic if all recording schemes could make their data available like this.

 

 

Urban Spiders

A new paper shows that Steatoda nobilis and Zygiella x-notata typically made up more than 80% of the urban spiders in an Irish survey. 

Collier, B. L., Leonard, D., Lyons, K., Dunbar, J. P., Lawton, C., & Dugon, M. M. (2026). Survey of Synanthropic Spiders in Ireland Reveals Expansion and Dominance of the Invasive Noble False Widow Steatoda nobilis in Urban Habitats (Araneae: Theridiidae). Ecology and Evolution, 16(3), e73193.

https://doi.org/10.1002/ece3.73193

 

The spiders of Great Britain and Ireland: 2025 checklist

Maintaining a national checklist for a taxon as large as spiders is a monumental task and Alastair Lavery has again updated the UK list, last published in 2019. This update recognises 680 established UK species, an increase of 15 in the last five years. Particularly notable is the number of species in anthropic habitats (buildings) - many of these are surely on the edge, waiting until the climate favours their spread outdoors. Also of interest is the discussion around the yet undescribed spider Megalepthyphantes cf. collinus and Mastigusa where for the first time in a Checklist, I am honoured to be referenced (even if my name is only spelt right once :-)

Lavery, A.H. (2025) The spiders of Great Britain and Ireland: 2025 checklist. Arachnology, 20(3), 410-427.  https://doi.org/10.13156/arac.2024.20.3.8

Good Vibrations?

While I'm yet to catch up with the Wasp Spider, Argiope bruennichi, I have long puzzled over the stabilimentum, a structure produced these spiders to decorate their orb webs. A new study shows that stabilimenta induce negligible delays in prey perception for transverse vibrations and only minor delays for normal and tangential vibrations, primarily due to the added inertial mass. However, for tangential vibrations, the presence of stabilimenta may enhance the spider’s ability to localize prey due to increased connectivity at the center of the orb web. It's an interesting finding but it doesn't eliminate the possibility of other functions, such as making these large webs more visible and so less subject to damage by animals blundering through them. 

Greco G, Dal Poggetto VF, Lenzini L, Castellucci F, Pugno NM (2025) The effect of different structural decoration geometries on vibration propagation in spider orb webs. PLoS One 20(10): e0332593. https://doi.org/10.1371/journal.pone.0332593

 

Contradictory spider

I recently wrote about microbiome-mediated spread of the Mirid bug Apolygus lucorum. Hot on the heels of that discovery comes another - the microbiome of the invasive Linyphiid spider Mermessus trilobatus does not contribute to its dispersal and spread. 

Complicated, isn't it? 

The Microbiome of an Invasive Spider: Reduced Bacterial Richness, but no Indication of Microbial-Mediated Dispersal Behaviour. (2025) Microbial Ecology, 88(1), 70. https://link.springer.com/article/10.1007/s00248-025-02565-6

 

What's in a name? The Tangled History of the "Charnwood Spider"

Like it or not, we need to start with some history (and taxonomy - sorry). 

Mastigusa diversa - a troubled past   See: https://wsc.nmbe.ch/genus/776/Mastigusa

• The name Cryphoeca arietina was first used by Thorell in 1871, having been previously misidentified as Hahnia pratensis by Menge. 
• This species was then identified as Cryphoeca diversa by Octavius Pickard-Cambridge in 1893. 
• In 1908 Pickard-Cambridge renamed it Cryphoeca recisam.
• In 1913 after wandering around Sherwood Forest, A.R. Jackson renamed it again as Tetrilus recisus (On some new and obscure British spiders. Transactions and Annual Report of the "Nottingham Naturalists' Society" 60: 20-49). 
• In 1937 Eugène Simon renamed it Tetrilus diversus, and in 1953 Locket & Millidge called it Tetrilus macrophthalmus.
• In 1986 Wunderlich changed the genus (again) to Mastigusa macrophthalma, based on taxonomic priority from the species name Tuberta arietina macrophthalma used by Chyzer & Kulczyński in 1897. 
• Which brings us to the taxonomic revision by Castellucci, Luchetti & Scharff in 2024, which suggested that UK specimens were likely to be a new species, Mastigusa diversa. (See: Charnwood Confusion Continues).

Enter DNA. Based on the results of Castellucci et al, my initial hunch was that UK specimens would end up as Mastigusa arietina. But this is Mastigusa we're talking about, and it's not that simple. M. arietina was about to disappear from the UK Checklist, not having been recorded for 100 years (UK specimens having been called ... M. macrophthalma - see above!). Thanks to the Tanyptera Project at the World Museum in Liverpool, DNA barcoding has now been carried out on specimens from across the UK. One of the specimens has in fact turned out to be M. arietina, but most UK specimens are Mastigusa diversa as predicted by Castellucci et al. But what about the Charnwood Spider? The Tanyptera Project says: 

"Mastigusa (Charnwood) - the DNA was sequenced successfully and at a high quality. ... Following these results, the results of your previous Mastigusa, and the papers you provided us, we are confident that this is likely Mastigusa diversa."

You would hope that this DNA-supported moniker now persists. The spider, nor its Spanish cousins ... doesn't care. 

With grateful thanks to Richard Gallon, BAS Spider Recording Scheme, for organizing this work and the Tanyptera Project at the World Museum in Liverpool for carrying out the DNA barcoding and funding it. 

Castellucci, F., Scharff, N., & Luchetti, A. (2023) Molecular systematics and phylogenetics of the spider genus Mastigusa Menge, 1854 (Araneae, Cybaeidae). Molecular Phylogenetics and Evolution, 107833. 

https://www.sciencedirect.com/science/article/pii/S1055790323001331

 

Whole Notta Love (In the Opiliorium)

I recently collected some Harvestman from a site I visited in order to identify them. Because I didn't have time to look at them immediately I knocked up an impromptu temporary Opiliorium (noun, a naturalist enclosure for the observation of Opiliones) (well it's a word now) consisting of a ventilated plastic box, a piece of wet kitchen roll and some apple peel on the bottom, and an arrangement of shoots for climbing on (being able to choose their own level is important in helping them to choose their own humidity level, from damp at bottom to drier at the top where the vents are). Because this was temporary housing I didn't add any substrate other than the paper towel or any food other than the apple. 

Immediately on introduction most of the inhabitants made themselves fairly scarce, but the pair (well, a male and a female) of Opilio canestrinii were very active, climbing around and doing laps of the enclosure. After an hour, they had settled down in the upper reaches of the enclosure, snuggled up with the second leg of the male resting on the female's abdomen. And so they remained until it got dark. 

I checked on them a few times after dark and the male was enthusiastically pursuing the female around the enclosure; she was equally enthusiastically running away, and that was the pattern each time I looked at them. The Dicranopalpus in there skittered around trying to keep out of the way and the Oligolophus hanseni hunkered down in the lower reaches and tried to get some sleep. I suspect they were unsuccessful in this, as was the male in his endeavours. 

The next day I examined and identified the specimens and released them. The downside of the translucent plastic box was limited visibility and I'm very tempted to set up a more long term Opiliorium in a glass aquarium for observation. From my limited experience I'd say the enclosure needs to be as big as possible in order to observe more natural behaviour. These fascinating Arachnids are surprisingly active given the chance.