UPDATE: this old post has been getting a lot of hits these past couple weeks, so it must be a problem for a lot of people, and so here's an update for 2015.
The catnip plant that had all the aphids on it last year didn't grow back this year, so I guess the aphids eventually kill the plant. Then again, I've lost a couple other of last year's catnip plants just due to root rot. No big deal, it's a weed and spreads like crazy.
The black ants who were farming these aphids have moved on to another catnip plant, but I've found I can get rid of them by spraying them with a pyrethrin-based Raid. However I don't want to do that, because catnip also attracts a lot of rare species of bee that you never see elsewhere, and I don't want to kill them with the pyrethrin.
Some people say you can deal with the problem simply by spraying off the aphids with soapy water. Well, it seems the black ants go and pick up all the aphids, clean them off, and plop them right back on the plant.
One other thing you might want to do, to take the fight to the enemy, is look around for large anthills: this species of ant seems to build big colonies, at least a foot across. There's even an ant colony in the neighbour's backyard that's a foot high and two feet across! I've been repeatedly destroying these anthills, wiping them out by turning a strong hose on them for half an hour to wash away everything, and yet they still come back. It's a war of attrition, but it satisfies the mass murderer in me, so I'll keep at it.
Oh and diatomaceous earth seems to do nothing to this species of ant. They're hardy buggers.
So here's the rest of the old post:
So I'm growing some catnip around the house for neighbourhood cats.
Also, it's been fun because catnip flowers attract lots of strange insects you won't find anywhere else - they love the nectar, so they come from miles around. I've seen lots of interesting species of bees, plus a few nice butterflies and some other strange bugs too. It helps improve biodiversity and gets cats mellow, so why not?
Anyway, one of the women at the pet food store said that catnip drives away ants, because it's a mint and ants hate mint.
Well, I can call bullshit on that. For a couple weeks I've had medium black ants* crawling through the catnip, supping at the little flowers. So they don't mind catnip at all. OK, fine, I says; the kitties can eat you and get some extra protein.
Now, however, it's gone one step worse.
I've had black ants farming aphids on the plants in the back for years. Basically, aphids seem about as stupid an insect as you can find, outside of scales; so ants just pick them up, carry them over to a plant they like, then plop them down like livestock on a pasture. The aphids drink from the plant's stem, and then the ants come by and lick the aphids' asses to get at their sweet sugary poop.
No really, look it up.
But now those black ants from the back have moved over to the side of the house where one catnip plant is, and now they're farming aphids on my darn catnip.
Screw you guys, pay rent or GTFO, I says. Bloody socialists.
Yeah I know, you don't believe me, so here's a photo for proof:
|click to make even bigger|
My digital camera can't focus in tight, so this was about the best shot I could take. The plant is catnip, obviously. You can see the ants, of course. The little gray blobs on the stem (where the most ants are) are the aphids, trust me on that.
Here's another pic, you can see the aphids a bit better:
|chlick to transform to yet greater proportions|
So just now I've powdered the aphids with diatomaceous earth. It apparently takes a long while for diatomaceous earth to kill aphids, but at least the ants will sod off and die pdq.
Anyway, if you don't believe the intelligent ants farming herds of aphids thing, despite this photographic evidence, then you can watch this short edumacational video:
And "harvest the gleaming secretions" is a euphemism for "licking their poop".
Come to think of it, it would also be an awesome title for a Godspeed You! Black Emperor album.
* - I don't know the species, but I call them "medium black ants" because they're larger than small black ants, and smaller than the large black ants.