by Troels Holm
September 21, 2018
A food packet for the child
One sunny day in July I was walking on a sandy track along the lake. Suddenly something green came tumbling down the slope and landed just beside me. It was apparently a moth larva. Fat and beautiful in shape and colors. It must have slipped from its food plant above, I thought at first. But suddenly I realized a strange thing. It was completely motionless.
Any normal larva should have struggled to get back into the shadow and avoid being exposed to lurking enemies in this way. But not this. My growing suspicion was confirmed as I looked farther up the slope and discovered this insect desperately looking for its missing prey. I had read about this burrowing wasp and its behavior but never observed it in action. Now I was in the middle of the drama.
The main character is the big (more than 2 cm) Ammophila sabulosa, the Red-banded Sand Wasp, of the hunting wasp family Sphecidae. The female wasp digs a tube shaped nest in sandy soil. Then she searches for a big food packet for her offspring. Typically a big larva of a moth. If only smaller specimens are available she collects two or more for the same kind. In this case a big larva of The Marbled Brown (Drymonia dodonaea of the moth family Notodontidae ).
When she localizes a larva she paralyzes it with a sting of poison. Since the larva is not killed, only immobilized, it will stay fresh for several days.
The wasp quickly finds its prey again and starts to carry it back to the nest hole.
Transporting such a big larva is a challenge. But observing how the wasp manages this task reveals much of the rationale behind the odd appearance of this animal.
The long and strong mandibles (jaws) are capable of a solid grip around the larva body and carrying a large weight. The long legs make it possible to lift the body sufficiently from the ground while carrying the fat larva below the body. The first pair of legs is somewhat shorter. With larvae of this size they can assist in carrying the larva and move it along.
The long and thin stem of the abdomen not only removes the abdomen out of the way from the space required by the larvae. It also makes it possible for the wasp to use its abdomen to support the larva and help in keeping the balance on the slopes.
After trying several impossible routes, she at last succeeds in bringing the larva back to the nest hole again.
But how do you carry the larva down the hole? The opening is not big enough for both of them.
The larva must be pulled by the end so the grip must be shifted. This is probably the moment where the larva rolled down at the first attempt. But this time she is more careful!
Quickly the larva is being pulled down the hole and out of visibility.
We can’t follow her further down so we must seek in the literature to get a glimpse of what happens in the dark.
Deep down in her cave the wasp arranges the larva in the nest and places an egg on it. After a few days, the egg will hatch and the new wasp larva will begin to eat the still alive moth larva. After finishing eating the wasp larva is big enough to pupate in the same nest.
But the hole must be covered as fast as possible before any parasites (flies or wasps) or competing females discover it.
The sand above the hole is quickly shoveled down by means of the long mandibles.
The material is pushed down the tube and compressed.
The opening to the cave (just below the abdomen) is now almost covered.
The wasp suddenly flies away and disappears for a while. She returns by foot several minutes later carrying a big plug by her mandibles. Perhaps a stone or a chunk of clay.
The plug is placed in the hole and pushed further down and more sand is added.
Everything is thoroughly stamped with the head and mandibles. I could really hear the thuds! At last some more sand is spread over the area.
The only traces left are the cavities above the nest from where the sand used for filling has been removed. And after one last inspection the result is approved.
From now on the offspring is left to its own. The mother is ready to build a new cave for a new egg.
Interested in technical details?
I took 233 pictures during half an hour. The conditions were far from perfect. I only had my 50mm f:2 macro lens. Even with a cropping factor of 2 on my Olympus E-620 camera (giving a field of view like a 100mm tele on a 35 mm camera) I was often afraid of getting too close to the sharp eyed animal. Most of the pictures have been cropped considerably.
Sunshine made it possible to photograph at 1/250 sec. and f:11. Unfortunately a few clouds disturbed and forced me to take longer exposures and use bigger apertures. Many of the pictures (or parts of them) were blurred due to the very fast moving animal, my own handshake or focusing on the background. You got the best.
A visit to Tiger Beetle Town
A few years ago on a holyday to the Danish island Laesoe I had a funny experience. I had a walk on a sandy track when I suddenly found this robber fly sitting on the ground.
I got closer very carefully with the camera and while looking in the viewfinder I suddenly realized that it was dead and had its entire head buried deep in the ground. Had it been trapped trying to catch an earthworm? I mounted the camera on a tripod and got a sequence of pictures for focus stacking.
And then I discovered another fly suffering the same fate. And this animal was obviously emptied. Just the shell was left.
Looking around I observed lots of holes, probably more than 100 nice, almost circular holes around 4 mm in diameter and without sand or soil around the rims.
That rang a bell. The mystery was solved. I stood in the middle of a Tiger Beetle town.
If you just walk past and look down you will discover holes magically appear a few meters in front of you. If you mange to stay motionless for a few minutes the holes will disappear again as the larvae slowly reappear at the surface. Their head and the shield of the first body segment add up to a round plug nicely filling the opening of the hole making it practically invisible on black soil. The rest of the larva is soft and white and hidden underneath. This is the larva of the Tiger Beetle (Cicindela).
When small insects pass near enough, the larva stretches out, catches the prey with its mandibles and pulls it down if it is not too big. In any case it sucks the body juices out of the prey.
I really wanted to get a focus stacked picture of the larva itself, but the slightest motion in a distance of 3 meter makes it disappear down its hole like a flash. And a flash makes it disappear just as fast. Each time you have to wait 2-3 min. And my 50 mm macro lens was simply too close.
I had to leave this wonderful place without my portrait picture. I had seen these holes before at several places, but far from my home.
And then it happened, as so often before: A natural phenomenon seems rare and strange until you learn to recognize it. Then you suddenly see it frequently. Back home I discovered a location with more than 25 holes just 15 min. walk away at a track I had walked several times before.
With an adapter I mounted my 40 years old beloved Vivitar 90 mm macro to my digital Olympus camera to get sufficient distance. No flash, no direct sunlight creating reflexes. I found a hole in the shade with a not too anxious animal. Tripod, focus rail, wire release. 62 all manual exposures at 1/15 sec, f:4.5 and subsequent stacking.
After living like this for 2-3 years it is big enough to enter the pupae stadium and eventually develop into the adult beetle.
Capturing the adult beetle picture is as much of a challenge. It hunts on warm sandy surfaces using its sharp eyes and fast legs. It is very alert and constantly on the move. Most pictures are taken while the beetle is eating and hesitant of leaving its meal. With a 200 mm tele I was lucky to get a picture of the hunting creature.
Another insect with long legs, but for a completely different reason. Here the purpose is to lift the whole animal the extra mm above the hot sand where the air is a few degrees colder, thus enabling it to keep a high activity level without being overheated. And of course you can run faster with long legs.
This is from a third location so I am not sure it is the same species. We have three species of Cicindela in Denmark, two of which are rather common on sandy locations. I am not able to identify the larvae to species but this brown adult is Cicindela hybrida.
From early in my childhood it was evident that I had to study biology. During my studies I borrowed a SLR-camera (Single Lens Reflex), the legendary Minolta SRT 101. I bought a cheap set of extension tubes and a reversal ring and did my first exciting experiments with real macro. When I later got a 90 mm Vivitar macro lens (infinity to 1:1) I was hooked.
During the last two years I have studied modern macro photography. My most important sources have been:http://www.photomacrography.net/ for forum and discussions of the latest developments, and http://extreme-macro.co.uk/ with an encyclopedic collection of everything worth knowing.
With inspirations and ideas from these sites I have built my own focus stacking studio. But I have chosen to show you two series from my field work because that is what I like most. They are both illustrations of the importance of biological knowledge and experience.
You can take a walk and use your eyes, but if you don’t have any prior knowledge of the behavior and ecology of the organisms living around you, you might very well miss the most funny and interesting moments.
Troels Holm is from Denmark and his interest is primarily in biology and macrophotography. For many years he worked with education and interpretation of nature and environment topics, often using his own photos as illustrations. After some following years living far from nature and with not so interesting occupations he has now retired and his love for nature and photography is now an important part of his life.
Thanks for looking!
If you want to see more of my pictures you are welcome to visit: https://www.flickr.com/photos/138612307@N08/albums