Since supporting the caterpillar stage of life is a big part of monarch gardening, we’ve expanded caterpillar hosting and helping segment of the monarch friendly gardening mini-series to break out more detail on some of the bigger issues with hosting healthy caterpillars, including steps we’ve taken in the garden for deterring their pests and predators.
Know Your Local Monarch Caterpillar Enemies
Different regions will have different monarch caterpillar pests and predators. Consult with your local monarch websites for information and keep a watch for unwanted visitors in your garden.
The War on Wasps
In our garden, the most visible threat comes from wasps. We have a number of wasps here in NZ that are problematic for the monarchs (read more at Monarch Butterfly Trust NZ). We have previously coexisted with them in the garden without an significant issues, but I’ve never seen anything quite like the prolific population of paper wasps here in the new neighbourhood. Pesky invaders!
Our success at attracting monarchs to lay eggs was like opening an all-you-can eat caterpillar buffet for paper wasps, and these habitual devils are recidivist offenders that return to successful foraging areas, so the fight was on to protect our caterpillars.
We immediately covered one area of our swan plants with the Popadome I’d received when I purchased our glasshouse. Safe from raids… Or so we thought! We quickly realised that although the paper wasps were too large to fly through the mesh, the sneaky devils were still small enough to perch and carefully slip in and out with small caterpillars to bring home for feeding their evil little wasp babies. Arrgh! I just happened to be out to photograph a few things nearby when I caught this %$@# in action. I managed to (foolishly perhaps) annoy this wasp enough by shaking the mesh around him so that the caterpillar fell free, but many had already been taken.
Protecting Our Monarch Caterpillars
A rush order for a fine insect net add-on for my Popadome finally put a stop to their thieving (and to most of my failing cursing at wasps…sorry, neighbours!), but I still have to be extremely careful not to let any sneak inside when temporarily unzipping the covers for access. Wasps are often hovering nearby waiting for their chance.
We also regularly search for and remove nests from the house, fence line, and other prime nest-building location. Yes, wasps can be beneficial, but here in NZ they are considered an invasive pest. The Department of Conservation and most local and regional councils actively encourage wasp control. Unlike common or German wasps, paper wasps seek live prey so the usual baiting wasp control use by authorities don’t work. Wasps and nests must be targeted individually.
Although we installed the netting system for wasps, it also reduces the exposure of caterpillars to many of the other potential pests and predators in our local area, such as mantids.
For those caterpillars who don’t wander out on adventures when ready to pupate, it also offers some protection to vulnerable stationary crysalides and newly eclosed butterflies. Although the structure is excellent for access control, I often find caterpillars (especially big mature ones) that have decided to slip out underneath and take themselves to nearby uncovered milkweed and/or to pupate in interesting places all around the garden… but more on that another time.
The Negatives of Netting
Because the netting also prevents butterfly access, eggs and/or caterpillars must be relocated into the enclosure. It also necessitates regular housekeeping, including cleaning up after our messy guests and pruning plants to maintain a suitable size for the enclosure. The difference it has made in our small caterpillar survival rate has been well forth the effort, though!
Different Degrees of Monarch Support
We allow our eggs, caterpillars, and chrysalides to remain outside, giving nature a helping hand by keeping keep a large garden supply of swan plant (milkweed), applying butterfly-safe garden practices, assisted caterpillar housekeeping, and reducing predator exposure risks.
To maximise egg-to-butterfly success, some folks like to raise caterpillars indoors. This can be particularly useful in less favourable climates and conditions. Complete environmental control allows the greatest degree of predator protection, but it also comes with the downside (unless you have unlimited space or time) of further concentrating the population in an unnatural environment. This requires limiting numbers, careful feeding, and significant care to reduce heightened risks of exposure to bacteria, disease, household chemicals, etc. It’s a personal choice either way, and indoor rearing can be excellent when done well.
A Stinky New Foe!
Update: We’ve been doing well with wasp control over the seasons/years since this post was first written; however, in the summer of 2020 a new pest was spotted. Young instar predatory stink bugs (shield or soldier bugs), were making a move on my monarch caterpillars. These pests attack much lager prey, like my caterpillars, by injecting them with a jab or toxic saliva before sucking on their innards. Nasty jerks. Mine appeared to be Schellenberg’s soldier bugs, a NZ native. Numbers were, fortunately, small. I’ve been inspecting the swan plants regularly and squashing any if found.