Black fly on broad beans

My Sister-in-law reports black fly on her broad beans (?Maybe black aphids?) in previous years.   She is in the UK and it has been very wet, and unseasonably warm, so the lawn has been mowed into paths around the edges of the suburban backyard to the raised gardens, leaving a large section in the middle where the grass is "very long".  This year the broad beans have no little black visitors, and she is crediting the long grass proving a distraction.  It would be interesting to know if this has been experienced elsewhere, with other plants acting as attractants, rather then the veggies.

Bearing in mind that the species may be completely different, I've never seen black aphids on any sort of grass . In previous years there have been some on my broad beans, but not very bad. The funny thing is there are two plants in my garden that are black aphid favourites: foxglove and wormwood. Instinctively I'd have thought they were the least attractive to pests.. The wormwood usually has grown quite a bit before any vegetables come up, and is attacked by the aphids quite early in the season. Ladybugs and little wasps find them a week or two after the aphids become noticeable, and some seasons the aphids seem unable to expand much. Other seasons the wormwood plants are visibly stunted by the number of aphids, but they have not been able to infest any of the vegetables much. I do have some flowering plants that are supposed to attract hoverflies and wasps, and help control pests that way, but the relatively early aphids on the wormwood is where I actually see a lot of predatory insects.
I did have too much wormwood at one point though, they grew in between other plants and seemed to keep especially pumpkins from thriving. It may have been competition, but possibly allelopathy.

The wormwood thing is interesting, it acts as a sacrificial host basically. I've heard the same about nasturtiums near beans, the blackfly pile onto those first and give the beans a bit of breathing room. Whether it's reliable or just luck probably depends on the year.

The Black Aphids that live in my ecosystem are definitely attracted to some plants more than others. My friend lost most of her broad bean crop to aphids one year.

In some areas, I actively see the ants farming the aphids. I think it's important to observe for that possibility, because if they are, you won't get rid of the aphids easily - the ants will have some in their nest. I'm suspicious that the ants prevent the Lady bugs from moving in also?