Advantages - Tyranids
What? Yes there are some. T6/W6/3+ based models are an advantage, regardless of the opposing army's ability to deal with them. If you can get those MCs into combat, Space Wolves as a general rule of thumb aren't going to be able to deal with them too easily. Add in bonuses like Lash Whips, boneswords and Old Adversary into the mix and the only units which can really go toe to toe with multiple MCs in combat are going to be TWC based units and often quite expensive. The problem with TWC here is they are often much better at simply chewing through lighter units such as Hive Guard, Termagants, etc. rather than actually staying units in combat. Whilst Tervigons and T-Fexes aren't that flash with WS3/I1, Trygons and Hive Tyrants, especially with Lash Whips, can be a scary thought in combat. The trick is getting them there.
This follows-on nicely to the biggest strength of the Tyranid codex regardless, combat. Whilst Grey Hunters are certainly better than their Tactical counter-parts in combat, they need to rely on cover to appropriately deal with Termagants, Hormagants, Raveners, Warriors, Genestealers and the like. Why? These guys are either hyper point efficient (Termagants with Tervigon buffs) or have enough attacks with bonus abilities (rending, boneswords, lash whips, etc.) at a higher initiative than the Grey Hunters that their increased combat abilities don't mean much. Wiping out small squads before they get to retaliate or to the point of uselessness is going to greatly help the little guys survivability.
Space Wolves will also find it harder to deal with these type of units (lots of infantry, T4/W3 models) whilst also effectively dealing with the tough targets. Many SW lists don't have a lot of ranged anti-infantry in their army outside of Long Fang missile blasts (which are busy killing T6 or T4/W3 creatures) and can often be forced to rely upon their Grey Hunters bolters and combat ability to deal with lots of little guys effectively. As we stated above though, the higher initiative and large amount of attacks means combat against these guys is not always an option.
The Tyranid psychic powers are a huge boon as well. Paroxysm is going to turn any unit into mince meat, even for Termagants whilst Catalyst is going to greatly restrict the damage the S8 AP3 missiles can do to monstrous creatures.
A lot of people point to anti-tank as a weakness of Tyranids but this is certainly not the case here. With the common chassis being the Rhino (AV11 based) Hive Guard + T-Fexes are going to be very effective in not only suppressing them but removing them from the game and exposing their contents. The LasPlas Razorbacks are a bit harder to deal with due to their range but T-Fexes can reliably suppress them whilst other anti-tank options such as Brainleech Devourers or Heavy Venom Cannons have potential as well. As usual however, it's the follow-up assault of MCs and rending units which will really hurt the low AV of the Space Wolves vehicles.
Tyranid players can also take solace in the fact that some of the units Space Wolves commonly bring aren't being used to their fullest potential. Wolf Scouts will find they have little use against Tyranids compared to their role against other armies but they are still more attacks in combat and can disrupt anything which is left in the backfield (i.e. Gant objective holders, Biovores, etc.). TWC aren't nearly as scary when one has lots of Boneswords and Lashwhips around as well as high strength + poisoned attacks in combat. Land Speeders are still great at blocking but are really no more use here than a Rhino though the extra MM shot at MCs and Heavy Flamer against gribblies is still annoying. One of the most annoying units for Tyranids though rarely sees play with Space Wolves and that's the Rifledread. The combination of the Rifledread + Long Fangs and LasPlas would be very hard to overcome indeed as the Rifledreads can focus on the Hive Guard whilst the higher strength/lower AP weapons can focus on the MCs. These don't often see play in Space Wolves armies however as they already have a lot of firepower in other choices. Rather, you'll see more midfield or combat elements where Tyranids are at their best.
Advantages - Space Wolves
One of the biggest advantage Space Wolves have, and no it's not lots of missiles, LasPlas or Jaws, is their ability to always dictate play. Whilst the Tyranid army might beat face in combat, particularly the little guys, they quite often require the ability to strike first and minimise the amount of damage they receive in turn (i.e. Genestealers, Raveners). In most cases this means not assaulting through cover and whilst this may restrict the Space Wolves army to being in cover, they still have their tanks to create mobility on the tabletop. This is also very important to dictating play as Tyranids cannot reliably stop tank shocks. Do you really want to death or glory with a Hive Guard or MC, fail and then lose the whole model? I wouldn't either (perhaps a change for 6th - MCs only take a certain amount of damage from failed Death or Glories?) and this means the Space Wolves player can run tanks at you willy nilly and always deny you objectives, slow your advance and generally disrupt your lines. All the while, their infantry are staying in cover (hopefully on objectives) and thus gain extra protection from most assaults. Space Wolves are good enough that striking before Tyranids means they can inflict quite a bit of damage and blunt the Tyranid combat advantage.
Then we get to the obvious stuff. Missiles, LasPlas and Jaws. Jaws is really the icing on the cake for Space Wolves and not really needed but it really hurts Tyranids. If I ran a Space Wolves list I'd much rather have Tempest or Hurricane as they are going to play a bigger role against more armies and Space Wolves already have an advantage against Tyranids without it. That being said, you will see it and it hurts Tyranids a lot if they are running Tervigons/T-Fexes/Hive Guard thanks to their low initiative. There are ways to minimise the impact is has upon the game such as not lining up your vulnerable units in neat lines and attempting to destroy the Rune Priest + unit. The latter however is difficult without much ranged anti-infantry and this is why Long Fangs are such an issue for Tyranids - they cannot easily access them and don't have a lot of ranged anti-infantry to drop them. The LasPlas are easily shaken/destroyed with T-Fexes/Hive Guard/etc. but those missiles will just keep coming and are protected from assaults by other units and tanks.
Now an average Space Wolves army can nearly drop a Tervigon in a single shooting phase with twelve missiles and four LasPlas Razorbacks with cover and no FNP and this is where Space Wolves really make their mark. A lot of Tyranid lists are based around tough, multi-wound creatures yet Space Wolves can down them pretty easily thanks to a lot of S8+ AP3- firepower. This firepower is pretty immobile however (hello Long Fangs) so being able to hide things for a certain amount of turns or limit the number of missiles coming into these units can greatly help the Tyranid list get across the board.
Whilst Space Wolves don't have a lot of ranged anti-infantry seen often in their lists, they do have options for this (i.e. stormbolters on Wolf Guard, small blasts from missiles, etc.) so it should not always be assumed they cannot reach out at hurt your smaller guys early. That being said, they do have excellent anti-infantry at short range with army wide combat ability and boltguns. As we discussed above, the use of terrain and vehicle disruption is important to maximise this potential but even if the smaller Tyranids break through the Space Wolves ranks or get clear assaults off on infantry units, there is enough shooting firepower to down the exposed unit (i.e. double tapping boltguns). This generally equates to the Tyranid player ending up trading units which is bad, especially considering the Space Wolves have the ability to counter assault (not the USR) with Grey Hunters, Wolf Guard, Lone Wolves, Thunderwulf Cavalry, Wolf Scouts, etc. and have more units to begin with thanks to dedicated transports.
Space Wolves also have much better psychic defenses with a basic 4+ on all powers. This is great for stopping Catalyst which can greatly improve the survivability of Tyranids against Space Wolves firepower but they also don't really have to worry about Shadow in the Warp either. It's short-ranged and doesn't affect the Rune Priest whilst inside a Rhino. The Rhino is shakeable sure, but having the 4+ psychic defense is very much worth it compared to casting Lighning or Jaws.
Overall Thoughts - Common Armies
The common armies (RazorWolves and T6'R'Us) present an interesting match-up on paper. The combination of the Long Fangs, Living Lightning and LasPlas Razorbacks are enough to on average, send a Tervigon to the grave but if the Tyranid player is able to hide units and cast catalyst on exposed units, the theoretical damage goes down greatly. The T-Fexes are what's really important in this match-up as not only do they reliably suppress the LasPlas RBacks at significant range but easily provide cover to the Tervigons and Hive Guard and can therefore advance in the open. Whilst the LasPlas + melta weapons can make mince meat of the T-Fexes with an alpha-strike, this tends to happen later in the game and the early missile fire at the T-Fexes is pretty useless thanks to a 2+ save. If the Tyranids can therefore advance across the board using the T-Fex durability to keep their Tervigons and Hive Guard alive long enough disable a lot of tanks and buff Termagants in combat, the game is strongly in the Tyranid's favor.
That's a big IF though, even with FNP + cover on the Tervigons, the Space Wolves have the firepower to down multiple Tervigons relatively easy. It might take more than one turn but de-buffing the Termagants is pretty important as they then become nigh on useless paperweights against MEQ armies. Remember as well, Catalyst after Turn 2 should always be casting through a Runic Staff and if not, the Space Wolves player is doing it wrong. The Hive Guard are harder to take down without lots of high rate of fire weapons (i.e. autocannons and heavy bolters) and this is what can lead to the RazorWolves undoing - a reliance on anti-infantry at close range. When all is said and done however, the RazorWolves have the obvious advantage, especially when we add Jaws (there goes that T-Fex cover) and no Tyranid offensive grenades to the mix but it's not an auto-lose matchup by any means. Some poor shooting on the Space Wolves player can have all your MCs hitting his lines intact but on the other hand, some good shooting can see your Tervigons gone by Turn 2 with your Hive Guard not far behind.
Conclusions
Space Wolves have the advantage, not rocket science, not game breaking news, it's a fact we've known for a long time. However, the divide isn't as large as one would expect (when we exclude Jaws) and whilst there are a lot of options for the Space Wolves player to control the board and destroy the Tyranid army, the Tyranids are not without strengths themselves. Playing to these strengths will obviously maximise your chances of winning but the divide between the two armies is always going to leave you on the back foot. The simple fact is, unless the Tyranid army gets lucky, they are going to be severely depleted by the time they actually reach the Space Wolves lines and you still have to navigate assaulting through cover, sacrifices and blocking.
Unfortunately, even going for a list with less reliance on large, multi-wound models such as lots of Warriors, Stealers, Raveners, Hormagaunts, etc. isn't likely to roll across a Space Wolves army and gimps itself against more mechanised foes. Whilst they generally do not have the ranged anti-infantry of other armies like Imperial Guard or Grey Knights without some dedicated thought and are vulnerable to these type of units if they strike first (i.e. not through cover), it's very easy for the Space Wolves player to force these units to assault through cover. The combination of striking last plus double tapping bolter follow-ups makes these units less effective than they would like to be and can overcome the lack of ranged anti-infantry Space Wolves lists generally bring.
Ultimately this is one of the harder match-ups for Tyranids due to the lack of durability their T6/W6 creatures experience, lack of ranged anti-infantry to access the Long Fangs and reliance on not assaulting through cover. Space Wolves have too easy a time disrupting the Tyranid movement (even though they have good anti-AV11 options), are good enough in combat that striking last is an issue against them and ultimately have the firepower to stop Tyranids in their tracks. Again, not unwinnable but certainly not a regularly winnable game.
