Whoo boy, here we go. After the trainwreck that is the Ethereal the last two installments have been fairly low-key; not so much how to make a bad thing good as how to make a decent thing better. But the fast attack slot contains arguably the worst unit in the whole of the codex, which is really saying something. That's right, today we're taking a good, long, hard look at...
The question 'what does this unit do' is perhaps nowhere more essential than with the Vespid. Because, quite frankly, what do they do? They're expensive, they're poorly armoured, they're average shots with close-range, low-output guns, they're average combatants, and if they lose their Strain Leader (sergeant) their leadership is completely in the tank. Usually, with a unit that's not quite competitive, you could just say 'cost cut' and make them at least moderately useful. But even if you could spam Vespid it's difficult to see how they could be useful, because they are simply, terribly designed.
Here's the problem. To be of any value, Vespid have to get close to their target; their guns have a 12" range. And since they're one of the few sources of AP3 in the Tau Empire, presumably you're meant to use them to hunt Marines. To do that effectively you need to not only be within 12", but within 12" and with no intervening cover to give those Marines an invulnerable save only slightly worse than the one the Neutron Blaster is stripping away. But Vespid are only average shots, hitting half the time, and it's entirely possible for a full-strength squad of Marines to survive a volley of fire from a full-strength squad of Vespid. And what then? Well, the Vespid can charge, and with I5 they'll get to hit first, but they're not very good in close combat and they're not very strong, and when the surviving Marines hit back, and Marines will survive to hit back, their 5+ saves are not going to do them much good. They'll probably hang on for a turn or three before the odds whittle them down, and then maybe they'll make it out alive and even more maybe-ly they'll regroup and contribute something.
Given that a full-strength Vespid squad costs 188 points, that's pretty unacceptable.
So, what would make them better? Well, the answer to that lies in their purpose; to kill Marines. The gun they have to do this with is suicidally short ranged, but that's not necessarily a deal-breaker. Rather than increase the range, the Vespid would be well served by increasing their ability to kill up close. With T3 and a 5+ save they're clearly something of a glass cannon, so let's run with that. Giving the Vespid rending, for example, would go a very long way towards making them worthwhile. They'd be frightening indeed on the turn they attack, blasting through power armour and then charging in to tear the survivors to shreds, but they'd remain vulnerable to long-range fire, and anything they couldn't swarm and kill immediately would still have a good chance of taking them apart in return. They'd remain something of a specialist unit, still struggling to compete for space against Pathfinders and Piranhas, but at least that way they might beat out gun drone squadrons for a slot.
There's a second option, as well. At the moment the Vespid have Fleet, which is frankly useless; nobody is ever going to forego shooting to run and charge with these guys. Their guns are the only things worthwhile about them. Instead of Fleet, then, why not let the Vespid enjoy that most quintessential of Tau strategies, jump-shoot-jump? Jet pack Vespid would be significantly more survivable, especially if they held on to the Skilled Flyer USR, which would let them pop in and out of cover to deliver their close-range blasts into the most vulnerable of targets. It's not a bad change, but personally I prefer the first option. The Tau Empire already lacks any particular degree of variation in its units, and making another JSJ-anti-MEq unit wouldn't do much to alleviate that.
But the Vespid are bugs, giant space bugs with blisteringly powerful guns and diamond-hard claws that they use to tunnel through floating mountains. These guys should be terrifying on the charge, and squashable at all other times. It fits the fluff, and it fits their role on the tabletop, a rare win-win in 40K.