Delivering food for the future
Unusually among insects, many members of the order Hymenoptera (wasps, bees and ants) provide their young with both food and shelter from the earliest stages of development.
Paper wasps (Polistes humilis) feeding their progeny
Direct provisioning
Some hymenopterans (e.g. paper wasps, bees, ants) feed their offspring directly and progressively throughout their larval lives.
The young are totally dependent on ongoing care from adults.
They are housed in a nest, which provides protection from predators and the elements.
“Stash-and-forget” strategies
But for most wasp larvae, parental care is quite indirect.
The mother lays an egg on or in the body of a living insect or spider. That animal represents a stash of food to support the growth of the larva hatching from the egg - “future food” if you like.
The larva is left to its own devices when it comes to consuming that food. The mother plays no further role in helping it feed - hence “stash-and-forget”.
Larval life as a parasite
In some cases, the host animal that receives the egg (or eggs) goes about its usual business thereafter - moving around freely, feeding and behaving apparently normally.
However, its internal body parts are being gradually eaten away by the growing wasp larva (or larvae).
Eventually it succumbs to the depredations inflicted by its parasite - as happened to this caterpillar.
Cocoons of the Wonboyn Wasp (Cotesia wonboynensis), formed after the wasp larvae left the body of their host caterpillar and pupated.
Larval life as a quasi-predator
In another variation on the “stash-and-forget” strategy, the mother wasp stings her chosen insect or spider before depositing an egg on it - thereby immobilizing but not killing it.
That paralysed animal remains a living, fresh, ongoing source of food to nourish the larva after the latter hatches from the egg.
So, the larva could be considered a predator even though its mother did the hunting.
There are some excellent examples of this strategy for rearing young in the recent posts Nesting habits of a little-known-wasp and Neighbourhood watch.
These mostly involve crabronid wasps (family Crabronidae).
Larva of a Pison wasp (family Crabronidae) feeding on an orb-weaver spider. The spider, while paralysed, is still alive. While the larva didn’t catch the spider (that was the work of its mother), it certainly qualifies as a predator as it is eating it.
Spider wasps – another example of a “predatory” larva
Spider wasps (family Pompilidae) are quite distant relatives of the crabronid wasps. However, they too use the stash-and-forget strategy for rearing their young.
They hunt their eponymous arthropods as food for their larvae. The type of spider chosen varies with the type of wasp.
These wasps are a common sight in our forest from late spring to late summer.
They are in constant motion, running and jumping over the leaf litter, flicking their wings, searching for prey.
Some are relatively large, brightly-coloured insects like this Ferreola handschini, the Orange-collared Spider Wasp.
Ferreola handschini, the Orange-collared Spider Wasp.
When seen with prey, the wasp, which is always a female, either carries the spider in flight or drags it over the ground.
She transports the spider to a site where she builds a nest in which to deposit it. In some cases she co-opts the unused nest of another wasp or other insect. She lays a single egg on the spider before sealing it in a brood chamber. Some species sting and oviposit on the spider while it is still in its own burrow, which then becomes the nest for the wasp larva. Unlike many of the crabronid wasps, spider wasps supply each larva with just one prey item.
That much holds true for all spider wasps. But considerable differences in breeding behaviour are seen in different pompilids, which I’ll illustrate with two species from our forest - Fabriogenia and Turneromyia, the Zebra Spider Wasp.
Fabriogenia - a familiar spider wasp
Fabriogenia is one of the most commonly seen spider wasps - both in our forest and more generally in Australia. It sits at the top of the leaderboard of iNaturalist observations of Pompilidae in Australia, with 730 observations. Cryptocheilus bicolor is a distant second with 330 observations.
(The taxonomic status of Fabriogenia is controversial. Some workers place these wasps in a different genus Auplopus. If you want to play it safe, refer to them as a member of the tribe Ageniellini).
I used the iNaturalist dataset of 63 observations of Fabriogenia with spider prey to get answers to a number of questions.
What sort of spiders do these wasps hunt?
Does the wasp remove the spider’s legs?
How does the wasp carry its prey?
How does it transport it to its nest site?
What type of nest do they use for their larvae?
Spider prey species
In 20 cases, I could reasonably confidently identify the spider carried by the Fabriogenia wasp.
9 of the prey were Badumna (family Desidae, House Spiders), 7 Clubiona (family Clubionidae, Leaf-curling Sac Spiders), 1 Phonognatha graeffei (family Araneidae, Leaf-curling Spiders), 2 unidentified Salticidae (Jumping Spiders), 1 Isopeda (family Sparassidae, Huntsman Spiders) and 1 Venatrix pictiventris (family Lycosidae).
Badumna and Clubiona together account for 80% of the prey.
Here are images of 3 of these prey taxa, seen living free in our forest.
Spider leg removal and prey carriage
In a large majority of cases (48/63, 76%), the Fabriogenia wasp had removed all legs from its spider prey and in another 5 cases, the spider had only one leg left.
This is presumably a strategy to streamline the cargo for flight.
In only 5 cases did the spider prey still possess all 8 legs. Of course, the wasp may have removed the legs from these spiders after the photo had been taken.
Kerri has observed the process of leg removal in action.
In late October last year, she noticed this Fabriogenia spider wasp in the undergrowth, grooming herself.
Immediately after this, the wasp pounced on a motionless spider on the ground nearby - a male Isopeda huntsman spider.
We presume she had previously found and stung the spider to paralyse it.
The wasp’s first act was to sever the spider’s legs using her mouthparts. She cut all 8 legs at the same position, between the first (coxa) and second (trochanter) segments. This was very precise, clean work - there was no sign of bleeding from the wounds.
13:49 wasp lands briefly and grooms
Just 6 minutes later, the job was done. She then grasped the legless (and hapless) spider in her mandibles by its spinnerets. Holding her prey close to her body, she flew a short distance and landed amongst the sedges.
A couple of minutes later, she disappeared from view, as she hauled her prey through the vegetation.
Her method of carriage – grasping the spinnerets with the spider tucked in neatly beneath her body, belly facing belly – is a very common one for Fabriogenia.
It was seen in 45 iNaturalist observations; for example here, here and here.
Less frequently - in 10 cases - the wasp positioned herself on the spider’s back with her legs astride its body.
In those cases, she held the spider by its chelicerae. Here is an example of a female using that alternative hold with a wolf spider Venatrix pictiventris. Note that in this case the wasp had removed only 3 of the spider’s legs.
Mode of transport to nest site
It is clear that Fabriogenia can fly with its prey to the nest site - for at least part of the way.
We often see flying Fabriogenia wasps in the forest clutching a spider and were recently able to capture such a pair. This enabled us to identify the spider as a Badumna insignis. The wasp had done a very neat leg removal job on the spider.
In this iNaturalist observation, it was noted that the wasp flew away with its prey after first removing the spider’s legs. Evans and Matthews (1973) found that a Fabriogenia female carrying a paralysed wolf spider Venatrix pictiventris occasionally took flight with her prey.
If her prey is particularly bulky, the wasp may have no option other than to travel overland for most of the journey to her nest site.
What type of nest does Fabriogenia construct?
Like all other wasps in the tribe Ageniellini, Fabriogenia uses mud as the construction material for her nests.
We often see a Fabriogenia moulding clay soil into a ball, then flying off with that to her nest site.
Fabriogenia appears to be opportunistic in its choice of nest locations. Evans and Matthews (1973) reported a female using the abandoned nest of the wasp Sceliphron.
We have discovered nests in a variety of concealed spaces - both natural and human-made (e.g. a box housing plumbing.
In the example below, the female had built her nest on the underside of the shade umbrella on our deck. (Note that the umbrella was closed when the wasp was building the nest).
Her nest took the form of 4 thick-walled cylindrical cells fused together. Multiple larval cells in a nest appears to be the rule for Fabriogenia. Evans and Matthews (1973) found 8 larval cells in each of two different Fabriogenia nests.
We were concerned that raising and lowering the umbrella would dislodge the nest. So we carefully pried it away from the fabric and placed it in a terrarium. (Rather poignantly, the mother kept returning to the umbrella, presumably looking to add more cells to her nest).
We opened one cell on the day we collected the nest - 15th November 2021 - to find out what sort of spider the female had collected for her larva. The only trace of the spider was its fangs. The wasp larva had clearly fed well as it had already developed to the pupal stage.
25 days later, on 10th December, that pupa had developed into a beautiful, pristine new female Fabriogenia wasp - seen here walking around the terrarium. And additional adults later emerged from the intact cells.
iNaturalist observations show some of the other forms a Fabriogenia nest can take.
A spectacular example is this mud turret. Another of these is shown under construction. This photo shows a female apparently sealing a cell at the bottom of a turret, suggesting that these can house multiple cells.
Females have also been reported squatting in bee hotels. And a more free-form nest is seen here - a group of Fabriogenia wasps constructing nests in a creek bank.
Turneromyia - the Zebra Spider Wasp
So how does Turneromyia, my other chosen spider wasp example, compare to Fabriogenia in its larval rearing behaviour?
Note that Turneromyia belongs to a different subfamily to Fabriogenia – Pompilinae for the former, Pepsinae for the latter. And I should point out another taxonomic wrinkle. There is a Zebra Spider Wasp, Ctenostegus, which shows only subtle differences to Turneromyia. Some wasps identified as Turneromyia in iNaturalist observations may in fact be Ctenostegus – and vice-versa.
A journey with prey from beginning to end
I got an excellent opportunity to find out more about Turneromyia on 21st January this year. I chanced across an individual dragging a spider over the ground in an area of relatively sparse vegetation - providing me with a good view of proceedings.
This wasp’s prey was a male Social Huntsman spider, Neosparassus sp.
She was using a different method to Fabriogenia to transport the spider – walking backwards, dragging her prey with the spider’s dorsal side upwards, gripping its fangs with her mandibles. While she sometimes flapped her wings when manoeuvring the spider, I never saw her take flight while holding it.
The spider was missing its two rear left legs, but I suspect it had lost those before the wasp found it. As noted below in my analysis of iNaturalist observations, Turneromyia almost always transports its spider prey without removing its legs.
The terrain was littered with leaves and sticks, many of which presented substantial obstacles to the wasp’s progress.
When faced with a particularly large obstacle, like this stick, she put the spider down and repositioned herself to pull her prey over it.
This video shows the wasp carrying out this tricky manoeuvre and her progress through the next stretch of this challenging landscape. The first and most relevant part goes very quickly. Use the slider control on the video to step through it gradually.
Here are two other examples of challenges presented by obstacles. The wasp showed considerable ingenuity in solving these problems.
Parking the spider to inspect a candidate nest site
The wasp followed an irregular course with no clear indication that she was heading for a particular destination.
At 9:53:45, she came to a large twig, several metres from where I had first sighted her.
She placed the spider alongside the twig and flew off.
She flew in different directions in a 30-40cm radius around that site.
Suitable nest site found
10 seconds later, she flew down to a patch of soil between a pair of leaves and began to dig in the ground. There was no obvious pre-existing burrow at that site.
Just 8 seconds later, at 9:56:03, she stopped digging and returned to the spot where she had parked the spider.
She pulled the spider up to the top of the stick, perhaps to make it easier to find on her return.
She wandered around it for a few seconds, then flew back to her dig, continuing the excavation for another 2 minutes.
Regular checks while constructing nest
She returned to the spider at 9:58:30 and wandered around it for another minute or so, occasionally touching its legs. Note that the spider’s legs moved when touched, showing that it was definitely still alive.
The wasp then flew back to her tunnel site and continued digging for another 2-3 minutes.
She was clearly making progress - watch the dirt flying in the video as she excavates furiously!
On occasion she came to the surface with material in her mandibles.
Final stage of spider transport
At 10:02:51 the wasp had clearly finished her excavation, since she returned to the spider and began to drag it directly back towards her tunnel. That journey took just 21 seconds. She was clearly very familiar with the route now.
The female made a final check of the tunnel and surroundings once she had positioned the spider near the entrance. She chased off pesky ants before dragging it into the opening. Note that she pulls it in backwards so that its legs don’t snag on the entrance hole.
Backfilling and sealing the nesting tunnel
Once her prey was safely inside, the wasp came to the surface and began backfilling the tunnel. I presume she had laid an egg on the body of the spider before starting this.
She dragged soil into the tunnel with her front legs and mouthparts and packed it down with rapid vibrations of her abdomen. Sealing the opening to the tunnel took around 20 minutes - a major effort!
She flew off soon thereafter, at 10:26:35, leaving little if any evidence of her nest building activity.
So this Turneromyia female has placed just one spider - on which she has presumably laid one egg - in this tunnel. Given the amount of time and effort she has devoted to back-filling the tunnel, it seems unlikely that she will return to deposit additional prey and/or eggs.
After capturing her next spider prey, she will have to begin her search for a nest site from scratch.
Contrast this with Fabriogenia which returns repeatedly to the same site to add additional chambers, each with a single spider and developing larva, to her nest.
As for Fabriogenia, I used iNaturalist observations of Turneromyia with spider prey (n=27) to glean information about their nesting behaviour.
Spider prey species
9 different spider taxa in 4 different families - Sparassidae (n=21 individuals), Miturgidae (n=4), Lycosidae (n=1), and Clubionidae (n=1) - were observed as Turneromyia prey.
The most favoured spider taxon was Neosparassus sp. (n=9), followed by Isopedella victorialis (n=6) and Mituliodon tarantulinus (n=3).
So like Fabriogenia, Turneromyia uses a range of spider taxa to select food for her growing young. Each wasp has its favourites but the menu of the two species is quite different, with little overlap in taxa.
Prey carriage
In 20/21 cases where a Turneromyia was seen holding its prey, the wasp walked backwards gripping the spider by its fangs with her mandibles - in the same way as I described for the wasp above.
These images of a Turneromyia, seen dragging a miturgid spider Miturga agelenina through sedges near the coast at Beowa National Park, illustrate this mode of prey carriage. Thanks to Max Campbell for permission to use these images from his iNaturalist observation.
In the other case, the wasp dragged its prey (a Clubiona spider) in a similar way, but held it by the tarsus of its right leg I. The spider was lying on its side in these photos, so the wasp may have been manoeuvring it into a position to grasp its chelicerae.
So prey carriage is very different to the female of Fabriogenia, which holds the spider tucked in neatly beneath her body - with the belly of the spider facing her belly in most cases - as she walks forward.
These two wasps also differ markedly in the removal of legs from the spider. In 26/28 cases where a Turneromyia was seen with a spider, the spider had a full complement of 8 legs. In the other two cases, the spider was missing just one leg. In contrast, Fabriogenia removes all or almost all legs from its prey in 84% of cases.
Getting to the nest site
In contrast to Fabriogenia, we have never seen Turneromyia flying with spider prey. It is difficult to imagine how they could do this, given they do not remove the spider’s legs.
It is clear from my observations of the Turneromyia female above that she was following an irregular course when searching for a nest site, rather than navigating directly to a site she had previously chosen.
iNaturalist observations, which in almost all cases show just one or a few photographs, cannot reveal the search strategy used by the wasp under observation.
However one iNaturalist observation gives a link to an Instagram page, which does provide information about the female’s nest searching strategy.
The author reports that the Turneromyia wasp dragged its prey (an Isopedella victorialis spider) for several metres over an obstacle-filled terrain to a vegetation-sparse area.
Like my female wasp, she parked her spider while she began to dig a nest, which was about 60cm away. In this case, she dug repeated trial nests before choosing one of these as a suitable site in which to deposit her prey.
Again, like my wasp, while her dig was in progress she made frequent checks that her spider prey was still where she had left it. After finishing construction of her chosen tunnel, she returned to the spider and dragged it in the burrow.
There is a strong similarity in the nest searching and building strategy used by these two Turneromyia females - which contrasts markedly with that adopted by Fabriogenia.
Coda: A story of two spider wasps
So here we have two wasps - Fabriogenia and Turneromyia - doing the same special thing. They provide food for each of their larvae in the form of a paralysed, yet living spider. They stash that spider in a nest and lay an egg on it. A wasp larva hatches from that egg and gradually consumes the spider as it develops into an adult wasp.
However, there are substantial differences in how each species carries out its mode of larval rearing.
Why do they choose different spider species as prey? Why does one wasp cut off the spider’s legs and the other not? Why does one wasp fly with its prey directly to its nest while the other wanders around on the ground searching for a suitable site to make a nest?
All good questions for future research.
Reference:
Evans, H.E. and R.W. Matthews (1973) Behavioural observations on some Australian spider wasps (Hymenoptera: Pompilidae). Trans. R. Ent. Soc. Lond. 125 (1): 45-55