My Fennel is growing really well again this year. Already the swallowtails have deposited eggs and caterpillars have hatched. Last year they overdid that and overgrazed the plant. To my knowledge, only two caterpillars survived and I think only one successfully became a butterfly. They were eliminated by starvation, exposure, and predators. Just too many caterpillars for the supply of Fennel. When the Fennel grew back, I was careful to keep the numbers down and there was a small bit of success on a second batch.

This year, I wanted to avoid that so I spent a couple of days picking off eggs and leaving only about seven caterpillars. Well, now the wheelbugs aka assassin bugs are successfully doing their predatory behavior by eating the caterpillars. I can't seem to find the right balance. Wheelbugs are beneficial too. All good for the Fennel, I guess. It's growing and blooming well.

For two days now I haven't been able to find a caterpillar in the fennel. A very bloated wheelbug was easy enough to find. I also am not seeing any further signs of the foliage being eaten. I shouldn't have removed all those eggs, I think. I didn't know how efficient the wheelbugs could be. There are always some around, but this is the first year I've seen them on the fennel. It's early, so I expect more eggs later. I wonder if I move any wheelbugs to another plant if they will stay or return. Maybe they will relocate on their own now that they've harvested their garden.

I've never heard of anyone getting rid of the beauty before, are they THAT voracious of consumers?

The caterpillars ate the Fennel last year until it was reduced to just the thick stems at about 4" high. Eating that much meant they had stripped anything resembling foliage off the stems and then proceeded to eat the stems. That left them exposed and they would just disappear both night and day. I guess birds and other varmints at night found them. Only two managed to get large enough to make a chrysalis and they both crawled away from the fennel to find more shelter. They didn't have far to go to get into some daylilies. I watched them, but something found one and it was shredded one morning. The other made it to the butterfly stage. I think it's a function of only having a container of fennel rather than a meadow with stands of fennel. The butterflies laying the eggs can't distinguish the difference, so the balance between available food and the number of mouths to feed was way out of whack. So I tried to correct it myself by removing some eggs, but I hadn't figured on the wheelbug as a predator because they hadn't been in the years prior. I found one caterpillar this morning, but I'm not too hopeful because the wheelbug is still lurking down in the foliage.

Why didn't you bring them inside? I'm just curious, I've never heard of this situation unfolding like so

@needrain - I have to keep relocating my caterpillars on the fennel. No wheel bugs so far (knock wood).





This is what's left behind! I'm so glad they're enjoying it!

In my experience, Black Swallowtails don't have a good egg-to-food ratio. They lay lots of eggs because, as you saw, predators keep them in check. But they tend to lay more eggs than even the other Swallowtails. It's like they can't judge the size of the plant correctly. FYI, only an average of 1-2 out of every 100 eggs makes it to a butterfly. About the only way to ensure better numbers is to bring them inside and raise them.

@bhart90
Brenden, My Fennel is in a large container. Not really suitable for moving indoors. I don't have the time to tend to caterpillars and feed them by hand. I need the balance of caterpillars to the plant. That worked really well the first two years.


@GrammaChar
How do you mean relocating it. Do you have more than one source for the Fennel? If no wheelbugs are lying around to ambush them, in the past they've been pretty efficient at moving around the Fennel in the container without my help. My Fennel has done well and are reasonably large plants now. I have to give them water every day without fail or they'll just lay down, but, last year, mine got eaten way past the stage you have in your photo. I knew it wasn't good even before they reached the stage of your photo. I thought I'd taken photos, but I can't find any. Not a pleasant photography subject, I guess.

@mellielong
"It's like they can't judge the size of the plant correctly." Yes, exactly like that. They'll be back again, I think. And I did find the one living caterpillar today, so maybe it will survive to the end. I didn't find a wheelbug today, so maybe they have relocated to greener pastures. As in lots of wildlife, the mortality rate for the young is high, I'm sure. The wheelbugs are just doing what they do naturally. I'd be ecstatic if it was cutworms they were chowing down on for their meals

Yes, Donald, I have fennel growing in two locations. When one plant gets eaten down to the nub, I break off the stem (with caterpillar) and truck it across the yard to the new site. The cats don't seem to mind the move. Hopefully the used-up fennel will recover and put on new growth....
Melanie, those are really depressing statistics on the swallowtails. I wish I had the dedication to bring them indoors to raise them, but I'm just not up to cleaning critter keepers anymore. Thanks for all you do.

Char, that's for all butterflies. Some lay fewer eggs, some lay more. The largest butterfly in the world, the Queen Alexandria Birdwing, which is very endangered, was found to carry an average of 23 eggs, I believe. But the caterpillars host on a type of Pipevine that grows on the other side of the world, so I am assuming they have a certain amount of toxicity. But normally, insects lay hundreds of eggs because there are so many things acting against them.

Black Swallowtails normally lay a lot of eggs, but then again, most of the things they eat aren't toxic. Well, some of their native host plants are (like Water Hemlock), but the herbs we grow obviously aren't. I refer to them as herb-stuffed caterpillars. Birds tend to feed on them pretty hard.

I grow Rue since it can host both the Giant ST and the Black ST. I got my first eggs of the season today and they were Black ST eggs. Surprisingly, I could only find five eggs on about nine plants. That's really low. Usually, I would expect more like thirty eggs. At least. I'm lucky that my grocery store sells organic parsley and dill that I can feed the cats so I don't run out of food.

"herb-stuffed caterpillars"
I've got a big patch of parsley in case the fennel runs out. But the parsley will croak once it gets hot, so the caterpillars better hurry up and do their thing!

needrain,

You might consider planting a couple (or more) of RUE plants. The little cats can be moved to it if mama butterfly prefers to lay her eggs on the fennel. I grow both plants. The RUE will do well through the heat of summer and once established is fairly drought tolerant. It also has more leaf surface so will last longer as a food source.

Myles

While relocating caterpillars from spent fennel to new plants, this one showed its osmetrium.
No cats were harmed in this process.

(GRR ROAR!) haha great photo

I find the Black Swallowtail cats are the quickest to use their osmeterium. FYI, we tend to call osmeterium "stinkhorns" on here so if you see that word, that's what we mean. I always think of Black ST cats as angry caterpillars, but if I came naturally herb-stuffed and wasn't toxic, I guess I'd have to get mean, too.

Ha! And you know how to spell it correctly!!!

I was going to let that one go!

I have little cats on the Fennel again and I'm not seeing wheelbugs at the moment. Didn't see a batch of new eggs, so I don't know if these just hatched later or if they just didn't overload the plant. Maybe if these get big enough, I'll poke on them and see if they will flash that osmeterium for me. I haven't noticed it when I had them before.

Just don't poke them too hard, and hold your nose when you do it!

So, curious, do you guys have queen anne's lace down there? And use it? My field is riddled in it, might do swallowtail with monarchs this year