Ted and Judy

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An Easy to Build Wasp Hotel

My homemade wasp hotel

Installing a wasp hotel to provide homes for solitary mud wasps provides several levels of enjoyment: watching their industrious comings and goings; observing their behaviour and that of the many parasitic insects that loiter with intent around their nests. The mud wasps are predatory which adds the bonus of natural insect control, particularly of caterpillars.

Mud Wasps

Solitary wasps and bees are provisioners. The female either digs a nest in soil or uses mud, resin or plant material to construct their nests on suitably sheltered substrate (mud daubers and potter wasps) or in holes and crevices mostly in wood. Other materials may be used if they contain suitable spaces. Mud daubers and potter wasps construct nests of one or many cells. The solitary wasps nesting in holes or crevices mainly have nests with a number of partitioned cells.

Provisioners

All provisioners stock their cells with enough food to allow the larvae to reach the pupal stage. An egg is laid on the provisioned food and its cell sealed up; no further care is provided. A variety of provisioned food is used depending on the species: bees use a ball of nectar and pollen; wasps use other arthropods such as caterpillars, cockroaches, grasshoppers, flies, cicadas or spiders. The wasp stings the prey which keeps it in suspended animation (fresh for its larvae). The eumenids attracted to a wasp hotel are caterpillar predators.

Families Using wasp Hotels

Eumenid Wasp

The subject of this blog is the two families commonly using wasp hotels, Eumenidae and Sphecidae, the former is the most prevalent. Both use mud as their building material. The blog also includes information on those insects that function as larval predators or parasites within the nests of solitary wasps.

Eumenids are solitary black and yellow wasps related to the eusocial paper nest wasps, but not aggressive. They are safe to approach and will only sting if severely provoked. Members of both families are easily separated by how they hold their wings at rest.  Eumenid wings are folded longitudinally and held erect at a steep angle above their body. Sphecids do not fold their wings longitudinally and hold their wings flat across the top of their bodies. 

Construction 

You can take the easy way out and buy a ready-made wasp hotel or you can be adventurous and make one yourself. Outlets such as Bunnings or The Diggers Club have them for sale. We recently gave one from Bunnings a try and it is currently doing a good trade in both eumenids and sphecids: eumenids using the larger holes; sphecids the smaller. One construction method is to follow the pattern of the commercial hotels using sections of bamboo. Another is to perforate a block of seasoned hardwood with holes of various sizes. This is not a technical or expensive exercise and requires very little in the way of handyman skills – just cutting lengths of wood and operating a drill. 

Bunnings Wasp Hotel

The materials can include a hardwood log or a solid piece of milled hardwood, a base weight of wood or cement and a cordless drill. The milled hardwood can be purchased cheaply from any demolition yard, but make sure the timber is untreated and unpainted. A half metre length of either is sufficient, but it can be up to a metre. A drill is used to densely puncture the wood with holes of various sizes (5,7 and 9 mm) drilled to the depth of the drill flutes. This gives a rough proportion of depth to diameter and wasp size. The holes in the Bunnings house are deeper at 10cm and appear to be to the wasps’ liking so the choice is yours. The final step is to balance the hotel so that it remains upright by screwing a heavy base plate to the bottom of the hotel. This can either be a square cut from an untreated hardwood sleeper, a footing of timber in the shape of a cross or a square outdoor quarry tile of a dimension to suit the height of your hotel. The size and weight of the ballast will be determined by the height of your hotel, density of the wood used (e.g. eucalypt wood is heaver than pine) and its width. With so many variables these decisions are for you to decide.

OK so now that your wasp hotel is constructed where are you going to locate it?  There are a number of considerations. If you are fortunate enough to have a sheltered, but sunny, open spot your decision is easy. If you have a veggie garden then somewhere in its vicinity would be ideal or just anywhere in the garden. All the wasp hotels I have built have been located in sunny sheltered spots so I have no experience of what happens if the hotel is exposed to heavy rain. In the wild they must survive, but on mass in a hotel things may be different. To be sure I suggest purchasing a large plant pot saucer and screw it upside down to the top of your hotel. Choose the diameter of the saucer relative to the height and width of your hotel to give the greatest cover. Since wasps are attracted to orange choose a terracotta coloured saucer. In your decision-making be aware that wasps are the most active on hot sunny days, so it is important to have a source of water for the wasps to avoid dehydration and to mix with mud to get the right consistency for building. We have water bowls for birds and see the wasps visiting these regularly during the day, but failing that any small container nearby would do.

Tenants

It may take a week or so for the wasps to find the hotel so be patient. If you have no tenants after two weeks try a new location. Once wasps find it they will keep returning to it and so will their progeny. Previously used holes may be rejuvenated by reaming out the old mud using a suitably sized screwdriver or a cheap drill bit 0.5mm smaller than the original. Any remaining debris can be removed using a can of compressed air (available in IT stores).

Unwanted Guests

Once your hotel is up and running you will notice other insects loitering with intent around it. These are the chancers ready and waiting to take advantage of the nesting wasps. Some hang about waiting for the cells to be filled and then nip in before the nest builder lays her egg and lay one of their own. In some cases the interloper doesn’t have to enter the hosts nests, They have a long egg placer (sting), which can be inserted into sealed nests allowing egg deposition in the host’s cells. The host’s larvae are used as the food for some species and the provided food by others. 

A Cuckoo Wasp was observed loitering around the Bunnings hotel allowing its behaviour to be noted and photographs taken. These brilliantly emerald green wasps enter the host’s nest to lay eggs. 

The one photographed was paying close attention to a eumenid that was busy stocking one of the tubes in the Bunnings hotel. It loitered out of sight on the sides or underneath of the hotel peeking around the side occasionally to see what the host wasp was up to. When the host wasp departed for more mud or a caterpillar the Cuckoo Wasp appeared near the active hole and tested the interior with its antennae to check its progress. When the cell was deemed ready to be sealed the Cuckoo Wasp entered to deposit her egg in the cell. The Cuckoo Wasp larva hatches first and devours the provisioned food. If the host returns unexpectedly the Cuckoo Wasp relies on its very thick cuticle and its ability to curl up in a tight ball to protect itself.

More Photographs of these chancers will be added to this post as they become available.

Some Observations

  • In gathering mud the wasps accidentally include plant debris and seeds in the mud. Germinating seeds would pose a structural disaster for the nest and its developing larvae. To address this, wasp saliva used to moisten and mould mud in nest construction contains a germination inhibitor. If mud from a recently abandoned nest is rinsed in water any seeds found are still capable of germination.
  • The wasps mostly enter and leave the holes headfirst. The fit of wasps to their chosen hole diameter is tight so it is difficult to imagine how this is achieved. There were occasions when entry is tail first and this may be because the wasp is working at the outer most cells that make turning around difficult.
  • The wasps mostly enter and leave the holes headfirst. The fit of wasps to their chosen hole diameter is tight so it is difficult to imagine how this is achieved. There were occasions when entry is tail first and this may be because the wasp is working at the outer most cells that make turning around difficult.
  • The eumenids were provisioning their cells with small green caterpillars of about their own body length carried under their body.
  • I noticed that the wasps in the last (outer) cells emerge first i.e. in reverse order to that in which they were filled and sealed. I had lined some of the large holes in the Bunnings hotel with paper drinking straws, which allowed me to investigate this by withdrawing the straw. I discovered two things: the wasp only used about eighty per cent of the ten cm tube so they must be able to sense depth and use the space to a set depth; cutting the tube transversely across the middle I discovered that the remaining cells were still filled with very immature pupae. The latter indicates that the wasps emerge in reverse order to that in which the cells were provisioned and sealed. I don’t know how this is achieved. Perhaps the pupae remain dormant at a certain stage of development and are stimulated to continue development by sounds of the wasp closer to the front chewing its way out. The pupa I found in the central cell was very pale and far from reaching to adult colours.
  • The hotel may also attract some solitary bees that use a waxy resin to line and seal their cells. If your hotel has a few large enough holes (11mm) leaf cutter bees may be attracted. These line and seal their cells with pieces of plant leaves, which they cut from the margins of soft leaves. Regular circular holes along the margins of leaves indicates the presence of leaf cutter bees in your garden.
Leaf cutter bee excision marks on leaf margins

If you enjoyed this blog consider inviting these busy wasps into your property and enjoy watching their activity.

Update 14/03/20

The day after posting this blog I noticed some green caterpillars at the mouth of one hole. Half an hour later they had wriggled out and fallen to the ground. I surmised that the final cell was not sealed because the wasp was dead. Below two photographs of the caterpillars, which are roughly two centre meters in length. They wriggle if touched but make no effort to wiggle away.

Update 15/03/20

Today I photographed two insects to add to this blog. Both are very flighty and hard to catch at rest for photographs.

Bombyliid Fly

The black bombyliid fly with a spot of white hairs on the rear end. This family of flies are capable a hovering flight but are not in the same family as true Hover Flies. Their delta wing shape at rest and large eyes are easy ways to identify members of this family. Every time the flash went off the fly would launch into flight and much persistence was required to capture it.

Small sphecid mud wasp

The wasp above is a small sphecid with an orange abdomen obviously inspecting a hole much too large for it. I drilled a series of 3.5mm holes to accommodate this species and they are busy filling them.

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