It grows like a weed, but doesn’t spread like one. It’s easily tamed by pruning. Every year as the weather warms, as it did a week or so ago before it reverted to February, and the elderberry starts shooting out in all directions, blue-grey patches form on stems.
Aphids! The species is, appropriately, Aphis sambuci, the elderberry aphid, and also European as far as I can tell -- most of the literature Google provides is in European languages.
This cluster of bugs is the product of vigorous parthenogenesis; a female producing large numbers of first instar nymphs via viviparous reproduction. All are female, clones of mama. In late summer or fall eggs will be produced, some of which, lacking a single chromosome, will be male. This leads to sexual reproduction and egg-laying. In spring, the eggs hatch into females, which start reproducing parthenogenetically -- a successful lifestyle, but perhaps, ultimately, unfulfilling?
Upon hatching, the nymphs puncture the stem of the elderberry with their stylet-like mouthpart, piercing the phloem, which carry the sugary products of photosynthesis downward. The aphids don’t even have to suck; the pressurized phloem fluid flows on in. No wonder feeding aphids look as if they might pop. What comes out of their anuses (ani?) is also sugary, and is mined by ants. There were ants on this cluster of aphids but they fell off as I was arranging the branch for a photo. Inept hymenopterans.
In a different light.