June was a busy month for the spider lab. After a week spent frantically setting up all our new spider pets in the lab and getting experiments underway we packed our bags again and took off to south west China. Our destination was the Xishuangbanna Tropical Botanic Garden (XTBG) which is found next to a small town called Menglun in the Yunnan province. The gardens are so well tucked away in the south west corner of China that you can just about peek over the border to Laos, with Myanmar not far away on its western side either.
XTBG is surrounded by a large river, with multiple bridges crossing it at various points, connecting both the local town and the large research institute associated with the gardens. We stayed in a hotel in Menglun and walked each day across a big suspension bridge into the garden after a delicious breakfast of rice noodles in a soup packed with herbs and spices.
One of our goals was to collect Siler semiglaucus jumping spiders, the focal species for PhD student Zeng Hua. Siler are tiny but covered in intricately colourful patches. Zeng Hua doesn’t know yet what the role of all these colours are but she aims to find out and is particularly interested in how they are used by males to advertise to females during courtship. Siler semiglaucus and other species in this genus are quite common around much of South East Asia and China, including Singapore, and worth keeping a look out for next time you are in this part of the world. Keep your eye out on park-land shrubs and trees; we’ve had particular luck finding them in long grass.
During our time at the gardens we were hosted by Prof Yang Xiaodong, a scientist based at the XTGB Chinese Academy of Sciences. Daiqin and I were both invited to give seminars about our research, and luckily I had a few slides on the ready so took Prof Yang up on the offer. The only problem was that not only was I lacking any professional looking clothes to wear, the clothes I did have smelt like I had been in the field for days (because I had), but hopefully the giraffe weevil videos distracted everyone.
After our talks we were invited to an amazing banquet with a bunch of other scientists based at the XTBG. This was just one of many feasts we took part in during the week including a wonderful spread put on by ladies at a local Dai restaurant. Dai people are an ethnic minority in China and live predominantly in the Xishuangbanna area. Here they eat a lot of delicious wild vegetables (fern fronds, various roots etc) with their staple sticky rice. I also found their housing really interesting too, which usually comprised of two stories with the upper level dedicated to living space and the lower level used for storing livestock (we mostly saw chickens), food and transport.
One of the highlights of the trip was discovering the fireflies flashing their glowing abdomens as they emerged during the evenings on our walks home from the gardens. Fireflies have a slightly misleading name, because rather than being a fly, the mysterious glowing light belongs to several types of beetle families including the Lampyridae, Phengodidae, and Rhagophthalmidae. All of these beetles belong to the larger super family of Elateroidea, of which most familiar to many would be the click beetles. Fireflies use their distinctive flashing signals to locate mates of the right species, which is important when several species are flying around at the same time. Unfortunately I didn’t get any pictures but can recommend this great video which shows timelapse videos of fireflies in the night sky.
Another fun find was this ant-mimicking crab spider (Amyciaea forticeps). Like so many spiders, this species mimics ants and in this case the mimicry is specific to weaver ants (Oecophylla smaragdina). Morphological adaptations to looking ant-like are called myrmecomorphy and there are hundreds of examples of these among spiders.
There are several Amyciaea species like the one we found in China around the world, and there are multiple species that mimic Oecophylla smaragdina. In Australia this species of weaver ant has green gasters (the bulbous bit at the end of an ant’s body), but in Asia the gasters are red. Interestingly, the colour of the crab spiders in these two regions of the world match the colour of the ants; in Australia A. albomaculata is green, while in Asia other Amyciaea are orange/red (like the one we found, above).
Although not much work has been done on Amyciaea spiders, they appear to be “aggressive mimics“. This means that they mimic weavers ants so that they can blend in among an ant colony and use these ants as food. As well as matching the colour of weaver ants, Amyciaea also have two black dots on their abdomen which look like ant eyes and move in a jerky ant-like fashion.
Aggressive mimicry among spiders is not very common; most examples are considered Batesian mimics, where the spiders look like ants to avoid predators. Many predators have a strong aversion to ants because they can be dangerous; they can sting, bite and spray acid as well as being able to recruit their nest-mates to launch an attack on invading predators. Ants, therefore, are a useful model for a spider to look like if it means avoiding a larger suite of predators. One of the most predominant groups of Batesian ant-mimicking spiders are the Myrmarachne, of which there are about 200 species.
We commonly see Myrmarachne around Singapore, and on both of our spider collecting trips abroad. Like many ant-mimicking spiders, Myrmarachne have a constricted “waist” (their abdomen has a narrow part) and they usually wave their front legs to resemble ant antennae. The way they move is also distinctly ant-like, in that they run in jerky little bursts. All of this make them really tricky to distinguish from an ant and it has taken me a while to be able to spot them among their ant models.
Myrmarachne also tend to be highly sexually dimorphic, meaning that the males and females look different. Among these ant mimics the dimorphism is due to males often having very enlarged chelicerae (jaws), while in females they are comparatively reduced. These enlarged chelicerae sticking out of the front of a male’s head should make them less convincing mimics. However, it is hypothesised that males are still able to deceive potential predators by looking like an ant carrying something in its mouth (like a seed or piece of dead insect).
Sure enough, when Ximena Nelson and Robert Jackson at the University of Canterbury looked at predation rates on male versus female Mrymarachne spiders, they confirmed that males are still convincing mimics. Both male and female Mrymarachne were avoided by Portia, a spider which will hunt other spiders but avoids ants. However, when they did a similar experiment presenting Mrymarachne to an ant-eating spider they found that males were targeted more often than females, probably because they are perceived to be an easier catch by looking like an ant weighed down with food.
Not all ant-mimicking spiders look very convincingly like their models. Orsima ichneumon, the jumping spider from Malaysia that I am working on at present, has various ant-like features such as a constricted abdomen and erratic movement when running around the vegetation. They also have very elongated spinnerets (silk producing structures) at the tip of their abdomen which point in different directions such that one set looks like insect mouthparts, and the other like antennae. As the spider moves the spinnerets bob up and down on the substrate they are walking on making their rear-end look quite convincingly ant-like. These adaptations aside, what really makes Orsima stick out is their incredible colouration. These colours certainly take away from their ant-like appearance, and I am interested in how these colours (as well as their other morphological adaptations and behaviour) are selected for; what is important for mate choice (i.e. what are lady Orsima interested in) and what is used to avoid or deter predators? Hopefully I’ll know more about that soon!