Will Hawkes
E N T O M O L O G Y
Day 9: Tiny frogs, sexist leeches and web-building flies.
Heavy droplets hammering on the tarpaulin overhead heralded the start of our final full day in the jungle. Sinking to my ankles in the mud, we squelched over to breakfast before waiting for the rain to finish to start our cockroach project data collection. Picking up our Epilampra sp. cockroach nymphs we collected from the beach last night, we set up their arena again: Four rock piles were arranged at each corner of our tray arena, each a different colour relating to the colours found on the beach – red, grey, brown and white. From a human vision perspective, the cockroaches seemed most closely matched to the grey rocks in terms of colour. As the cockroaches hide during the day, if they show colour matching ability then it would be expected that they hide on or under grey rocks as they were most hidden in this location and so would best avoid predation. If there was no preference by the cockroaches to rock colour and they just hid in any of the piles, we could infer that the cockroaches are only looking for somewhere to hide under and don’t worry about colour matching.
We gave each cockroach three minutes in the arena and recorded how much time was spent under each rock pile. At the end of the experiment we looked at our data and found that, in contrast to our prediction, the cockroaches significantly preferred red rocks! And that the grey rocks were almost the least chosen alongside white rocks (see graph).
Results of our cockroach experiments
Because the rock choices were not random this suggests some sort of choice was occurring, but what? My current favourite theory is as follows.
Birds (cockroach predators) awake at dawn and so the cockroaches would have to hide before dawn while it is still too dark to discern colours. This means that rocks that reflect the least light (and therefore seem darker) may be the most effective hiding places – the non-reflective cockroach’s outline would show up most strongly on more reflective rocks (i.e. the white and the grey). Red light wavelengths are short and are perceived as very dark in low light environments (this is why many deep sea creatures use red as camouflage). So it is possible that the cockroaches are choosing the darkest rocks to shelter under.
However, this doesn’t really explain why the cockroaches still chose the red rocks during the day when the dark-ness of each rock should be roughly the same. Therefore, it may be that while the cockroaches have pretty good vision, they do not entirely rely on their eyes to find shelter. These nymphs have very long antennae which they use for a lot of touch interactions. Potentially the cockroach nymphs have learnt to determine the difference between the more reflective (smoother) and less reflective (rougher) rocks through natural selection and so choose the rougher rocks to survive. This obviously needs far more testing and experiments to find the answer but it is interesting to think about!
Epilampra cockroach nymph
The two projects in camp were not focussing on the most stereotypically adored animals. While I was looking at cockroaches, Ted’s group were studying whether leeches were sexist or not. Leeches were collected from around camp – this apparently was harder than expected as, of course, leeches were everywhere when you didn’t want them and nowhere when you did. Luckily, one of the Indonesian students, Blenda was excellent at leech herding and found lots for them. The group set up an arena on the ground and had the victims take their socks off and rest their bare feet at each end of the arena – a male at one end, female at the other. They found that the leeches consistently preferred males to feed on than females! This finding of sexist leeches was somewhat unexplained but could be answered by males having hormones that connoted tastier blood or just the fact that the males tested were less good at personal hygiene and so were more easily detected!
Brown leech - Haemadipsa zeylanica
By early evening we had finished all of our projects and were free to explore. A cross sticky frog was found on the leaf litter by Amber (see day 3 for my surprise when I grabbed one). This frog was likely feeding on insects but it may also have been searching for a place to lay its eggs. The frog is known to be a phytotelm breeder – it lays its eggs in small cavities that contain water in terrestrial plants. Amazingly, this species of sticky frog will sometimes lay her tadpoles in the water of carnivorous pitcher plants (Nepenthes sp.)! The tadpoles are tough enough to survive the digestive enzymes in the water and this makes it a very safe habitat for them to develop in.
A cross Rufous-sided Sticky Frog
Ted called me over to see a spider he had caught in a pot. The high cephalothorax (head/thorax) area which has an almost vertical face making it a spider in the Zodariidae family, maybe a Mallinella sp. but am very unsure about this. These spiders are ant predators and generally live on the forest floor where they chase down their lunch with their swift running speed. Males of some Zodariids have small lumps on the tops of their first three pairs of legs which may be used to create a sound during courtship!
A Mallinella species of Zodariid spider
Night was falling and it was almost tea time but one last hunt around the foliage at the back of camp revealed quite a strange spider. He is a Utivarachna fukasawana (described by a Japanese arachnologist – Kishida) and has made a silk house for himself to shelter in overnight. These spiders are armoured with a thick cephalothorax and abdomen. Not much is known about the lives of these spiders but they do mimic ants with their tubular extension of their cephalothorax looking a bit like an ant’s waist.
Utivarachna fukasawana
After tea we set off on our final jungle night walk off the trip, determined to make it one of the best.
It started off excellently with a huge red assassin bug from the Eulyes genus, potentially E. amoena. These bugs are predatory and have a long piercing mouthpart called a rostrum. The rostrum on this bug slots into a groove under its thorax. This groove has ridges in which the bug may grate its rostrum across, producing sound called stridulation. This sound may be used to shock potential predators into letting the bug go. When this bug is the predator, however, it uses this rostrum to stab into the prey, inject lethal saliva containing digestive enzymes, before using the rostrum to suck out the unfortunate prey’s insides! This saliva can be so potent that the bug can kill prey many times larger than itself.
Possibly Eulyes amoena assassin bug
A juvenile giant tree huntsman (Heteropoda boiei) with characteristically spotted legs watched us as we traipsed by. These spiders can grow to be massive and actually have gliding capabilities as we found out earlier in the trip at Sungai Wain forest (write up coming soon!).
Juvenile giant tree huntsman - Heteropoda boiei
On the leaf above a beetle closely related to the trilobite beetles was sat. Despite being from the same Lycidae family of net-winged beetles, this insect looks very different to the odd looking trilobite beetles (see Sungai Wain write up – coming soon!). The Lycidae family contains over 2800 species and is generally made up of beetles that are quite colourful, although this one is decidedly dark. They are generally characterised by a raised network of veins on their elytra (wing cases) and by flattened antennae. Their larvae feed on wet wood while the adults generally go for nectar or other insects.
Lycidae net-winged beetle
Despite promising to lead from the front tonight to show everyone as much as possible, I had still managed to fall to the back with just a few of the group. The rest had gone ahead with Ted to look for more reptiles while we climbed slowly, checking every tree for new invertebrates. A fog was closing in and the air was filled with water droplets, shimmering brightly in the torchlight and settling on the thousands of spider webs scattered everywhere throughout the trees. One of the more stereotypical spider web shapes (an orb web) was inhabited by a very beautiful little spider. Bright green and looking somewhat like one of those ice-gem sweets the spider was in the Araenidae family although I’m not sure any further than that!
Green Araeniid spider
Under a branch, facing downwards, was a delicate white/pink flower. We had seen so few flowers on this trip as the majority are way up in the canopy. This did seem to be trying to attract pollinators accustomed to the gloom of the understory with its bright white colours although why it was facing directly down was interesting. It may be that the flower had got it wrong or the branch had moved, but just maybe the flower is targeting pollinating animals that spend most of their time on the forest floor.
Pretty white nocturnal flower
Attached to a tough length of silk was one of the most beautiful animal-made structures in the forest – the cage-like cocoon of an Arctiidae moth caterpillar. This caterpillar weaves a hanging basket which is quite see through to protect itself while it pupates into a moth. The moth itself is from a family that has a specialised sound producing mechanism called a tymbal organ. This organ may be used in jamming bat’s echolocation to prevent them eating the moth.
Arctiidae moth cocoon
Mating Arctiidae moths
Another spider’s web caught my torch’s light. It was in front of a small hole in the bank which generally means an exciting spider. Grabbing a small stick, I gently vibrated the silk to entice the inhabitant out. However, my stick just went straight through the silk with very little resistance. Looking closer I realised that it was not a spider that had made this silken web, but a fungus gnat larva! This fly larva may be using the sticky threads to capture prey, even to the extent of using chemical lures!
Fungus gnat web!! You can just make out the larvae in the top left of the web.
Prowling the floor beneath was a real spider, and one that is apparently very rare – the tiger-striped medmassa Medmassa tigris. So named because of her tiger striped abdomen. Her long thin legs allow her to run quite quickly, probably hunting smaller insects such as ants but very little seems to be known about this creature.
Potentially the rare Medmassa tigris spider
Suddenly I spotted two of my favourite spider species waiting for food on the leaf litter, a male and female Sarawak wandering spiders (Ctenus sarawakeensis). These big spiders are relatives of the somewhat vilified Brazilian wandering spider in South America, famous for being the most venomous in the world. Like the Brazilian spider these ones are very gentle animals and are very happy to crawl over your hand if you’re careful. They are also thought to be less venomous than their Brazilian cousin and are in a different genus of the Ctenidae family (Ctenus rather than Phoneutria). The males especially are beautiful animals having shiny patches of hair on their legs and slightly iridescent fangs.
Male Sarawak wandering spider
Female Sarawak wandering spider
A shout from Ted as he crashed through the undergrowth towards me with the tiniest of frogs on his expedition watch. The pothole narrow-mouthed frog Microhyla petrigena – a Bornean endemic! These special little frogs are listed as threatened on the IUCN redlist and are found nowhere else in the world. They only reach 18mm (so a good 5 times bigger than this one!) and occasionally are called chorus frogs on account of their song when they mass together near swampy pools.
A tiny, tiny Microhyla petrigena frog feat. expedition watch.
The next animal was straight out of a certain wizarding world… a whip scorpion. Whip scorpions are in the Amblypygidae family and are fairly intimidating looking creatures with their long legs (the second pair are very long, thin and used as communication and sensory organs) and red-tipped fangs but have a couple of quite endearing personality traits. The expectant mother whip scorpion will lay up to 20 eggs in a membranous brood sac which keeps the young damp. For the next couple of months the female will carry her eggsac under her abdomen. When her young eventually hatch they look very similar to her but pure white. They then climb onto their mothers back and remain there with specialised suckers.
Amazingly, these young will remain with their mothers for at least a year despite being fully capable of surviving independently! The whip scorpions will remain together as family groups until the young reach sexual maturity at about 13 months when they disperse to find mates. It is thought that not only does living in these little groups reduce predation risk through combined defensive behaviour, but the whip scorpions may also direct their siblings and mother towards promising food sources through leg based communication!
Amblypygid whip scorpion
Almost back at camp I was dawdling at the back, reluctant to finish our last night walk, when a bright green creature caught my eye – an adult cicada was emerging from its juvenile exoskeleton! Despite hearing the cicadas all the time we barely saw any and so to see this amazing metamorphosis event was extremely lucky. Cicada nymphs spend years developing underground but only live for a short time above ground which is why they sing so enthusiastically.
Emerging cicada
Heading to bed I watched as Ted hopefully dotted about behind camp having one last, unsuccessful, hunt for horned frogs.